the system 500 shown in fig1 includes a derrick 502 from which extends a drillstring 504 into the earth 506 . the drillstring 504 , as is well known , can include drill pipes and drill collars . a drill bit 512 is at the end of the drillstring . a rotary system 514 , top drive system 526 , and / or a downhole motor 532 (“ fluid motor ”, “ mud motor ”) may be used to rotate the drillstring 504 and the drill bit 512 . a typical drawworks 516 has a cable or rope apparatus 518 for supporting items in the derrick 502 . a mud pump system 522 according to the present invention with one , two , three - to - ten , or more mud pumps 521 according to the present invention each with pumping modules with one or two valves according to the present invention supplies drilling fluid 524 to the drillstring 504 . drilling forms a wellbore 530 extending down into the earth 506 . each mud pump 521 has at least one valve 501 according to the present invention or ( as shown in fig1 a schematically ) multiple pumping modules 503 each with a suction valve 505 according to the present invention and a discharge valve 506 according to the present invention . each mud pump 521 has a main crank shaft 521 c . during drilling , the drilling fluid 524 is pumped by pump ( s ) 521 of the mud pump system 522 into the drillstring 504 ( thereby operating a downhole motor 532 if such an optional motor is used ). drilling fluid 524 flows to the drill bit 512 , and then flows into the wellbore 530 through passages in the drill bit 512 . circulation of the drilling fluid 524 transports earth and / or rock cuttings , debris , etc . from the bottom of the wellbore 530 to the surface through an annulus 527 between a well wall of the wellbore 530 and the drillstring 504 . cuttings and debris are removed from the drilling fluid 524 with equipment and apparatuses not shown , and it is re - circulated from a mud pit or container 528 by the pump ( s ) of the mud pump system 522 back to the drillstring 506 . also , some desirable solids may be added to the drilling fluid . a system 10 according to the present invention as shown in fig2 a and 2b has a main housing 12 mounted on a base 8 with an optional crane system 20 for lifting and moving system parts . a pedestal 21 of the crane system 20 is rotatably mounted on a bearing assembly 22 on the housing 12 . a lift apparatus 23 is movably mounted on a beam 24 and a support 25 extends down from the lift apparatus 23 . a chain hoist lift may be used with the structure shown which is attached to the support 25 . motors 14 each drive pinions 16 which in turn drive a drive gear 18 ( see fig3 c ) to move pistons 19 for six removable pump modules 650 ( as described below ; may be any module disclosed herein and / or may have any valve assembly or valve assemblies disclosed herein ). a pressure relief apparatus ( e . g . one or more relief valves ) is provided for the modules 650 and , as shown , in one aspect , for each of the six modules 650 there is a pressure relief valve 13 . optional rails 15 project up from the housing 12 . an oil pump 2 pumps lubricating oil to various parts of the system . a water pump 4 pumps water to a filtration system ( not shown ) and a cooler ( not shown ). the pumps are mounted on pump mounts 8 b connected to the base 8 . doors 3 and 5 ( one each for each pump system 30 ) provide access to various internal parts of the system 10 . drilling fluid enters the system 10 through an inlet 7 and is pumped out via the modules 650 to a main outlet 9 . the modules 650 have a body 602 with a first bore 602 a and a second bore 602 b . a discharge valve assembly according to the present invention is in the first bore and a suction valve assembly according to the present invention is in the second bore . with a piston fluid is pumped into a chamber 652 of the module 650 via an inlet port 604 and is discharged from the module 650 into a discharge conduit 634 via an outlet port 606 . fig2 f shows the relative positions of two valve assemblies 100 a , 100 b ( like the valve assembly 100 ) according to the present invention as they are present in a block of a mud pump module . the valve assemblies 100 a , 100 b ( which may be any valve assemblies disclosed herein ) are in bores 642 , 643 , respectively , in a block 644 . the block 644 can be used in a system like that of fig2 a . fig2 g - 2i show two valve assemblies 100 x , 100 y ( like the valve assembly 100 a , fig9 a ; may be any valve assembly according to the present invention ) as they are disposed in a block b ( shown in dotted line ; may be any suitable block or body ; including , but not limited to , the body 602 or block 644 referred to above ) of a mud pump system . fluid is sucked in by action of the suction valve assemblies 100 x through a suction inlet 400 and discharged by action of the discharge valve assembly 100 y through a discharge outlet 402 . the fluid is received in a pumping chamber 404 . fluid pumped from the chamber 404 can impact parts of the discharge valve 100 x . optionally , an accumulator / dampener 410 , positioned within the block b , is in fluid communication with the pumping chamber 404 . the accumulator / dampener 410 reduces undesirable pulsations of fluid under pressure from the pumping chamber 404 . any suitable known accumulator / dampener may be used . fig3 a and 3b show a valve assembly 100 according to the present invention which can serve as a suction valve or a discharge valve for a mud pump system ( e . g ., but not limited to , the suction valve assembly 680 and the discharge valve assembly 630 described above ; or the suction valve 100 x and the discharge valve 100 y described above ). fig4 shows top portions of the valve assembly 100 . the valve assembly 100 has a hollow cartridge stem 102 with an interior channel 104 within which are located a valve actuator 130 and an adapter 106 . a spring support 108 , connected to a flange 110 of the cartridge stem 102 , has an end 112 which is encompassed by part of an expansion spring 120 an end of which abuts the spring support 108 . a poppet ( or curved valve member ) 114 rests on a support 116 . an end 122 of the spring 120 abuts and is biased against a bottom of the support 116 . a ball 118 rests on a ball support 124 which rests on the support 116 . a cable 128 ( i . e . a non - rigid connector ) ( made of any known cable material ) connected to the ball 118 passes through a hole 140 in and through the support 124 , through a hole 142 in the support 116 , through the spring 120 , through a hole 143 in the spring support 108 , through a hole 144 in the adapter 106 which is and is connected to the adapter 106 connected to an actuator 130 . a washer 151 above the ball 118 abuts an underside 115 of the poppet 114 . a recess 152 within the poppet 114 houses the ball 118 , the washer 151 and the support 124 . the poppet 114 has a tapered surface 136 for sealingly abutting a valve seat and a seal of a valve seat as described below . the poppet 114 is movable toward and away from a valve seat 160 . the valve seat 160 has a channel 162 for fluid flow therethrough . the poppet 114 selectively closes off and opens up the channel 162 to fluid flow . part of the channel 162 is sized and configured for the poppet 114 . a surface 166 of the valve seat 160 is positioned to seal against the tapered of the surface 136 of the poppet 114 . optionally , there are no guide fingers projecting from the poppet 114 ( although it is within the scope of the present invention to use them ); and there are no arms or ribs across the valve seat ( it is unobstructed ) for receiving and stabilizing a rod , stem or neck projecting from a poppet ; and there is no rod , neck or stem projecting from the poppet . thus , flow through the channel 162 is unobstructed by such parts which are present in many prior valves . a recess 168 around the valve seat 160 holds a seal 169 . part of the surface 136 of the poppet 114 sealingly abuts the seal 169 when the valve assembly is closed , preventing fluid flow . thus dual sealing is achieved . the poppet 114 has a range of freedom of movement within the channel 162 of the valve seat 160 . however the poppet 114 is located within and with respect to the valve seat 160 , part of the outer tapered surface 136 of the poppet 114 will sealingly abut the seal 169 and the surface 136 will sealingly abut the surface 166 . the poppet 114 can be aligned ( or not ) with the valve seat 160 , but either way an effective seal is maintained with part of the surface 136 sealed against the seal 169 . movement of the poppet 114 on the ball 118 and the sizing and configuration of the various parts contribute to permissible freedom of movement of the poppet 114 without sacrificing the sealing necessary to close the valve assembly . fig5 shows the valve actuator 130 which can be , in certain aspects , any suitable known controllable , valve actuator , e . g ., but not limited to “ muscle ” apparatuses , pneumatic cylinder actuators , hydraulic cylinder actuators , and electromagnetic actuators . in one aspect , as shown in fig5 , the valve actuator 130 is a controlled , pneumatically powered actuator known as a festo ( trademark ) “ muscle ” actuator . the actuator 130 has an expandable hose 132 mounted between two bases 134 , 135 . air under pressure is introducible into the interior of the hose 132 through a channel 137 in a pneumatic coupling 139 . the upper base 134 is connected to an adapter support 127 to which the adapter 106 is secured . as shown in fig5 , air under pressure has not yet been applied within the hose 132 . once air is applied the hose moves outwardly , effectively moving the top base 134 toward the lower base 135 and thereby pulling the adapter 106 to pull the cable 128 and move the poppet 114 out of sealing contact with the valve seat 160 against the force of the spring 120 . fig6 shows one embodiment , a spring 120 a , of a spring 120 . as compared to prior known spring designs , the spring 120 a has a spring body with a smaller spring diameter , a , and with a higher spring force ; but the wire diameter is relatively large , e . g . 0 . 22 inches , which results in the higher spring force . use of an actuator like the actuator 130 , fig5 , makes it possible to use a spring with the increased spring force ( with the increased wire diameter ). the overall diameter , b , of the spring 120 a is relatively smaller than prior springs because the spring 120 a does not have to accommodate the relatively large necks of certain prior valve members . certain prior mud pump valve springs reached a known resonant frequency ( e . g . about 40 hz to 43 hz ) creating poppet oscillations that resulted in an improperly seated poppet and in fluid pulsations transmitted downstream of a valve assembly . due to its size and weight , the spring 120 a has a higher natural frequency than those prior springs which resonate around 40 hz and , thus , more force is required to resonate the spring 120 a . in certain aspects the spring 120 ( or 120 a ; or the spring 120 b , fig7 a ) is sized and configured so its natural resonant frequency is about 25 % higher than that of certain known springs ( e . g ., in one aspect 50 hz vs 43 hz ). this reduces the chance of flow - induced resonance in the valve assembly with such a spring ; provides better , more stable control of the valve assembly &# 39 ; s poppet ; and provides more positive seating of the poppet against the valve seat . fig7 a and 7b show a spring 120 b according to the present invention which has a spring body 120 c and an end tapered portion 120 d which abuts a support ( e . g . like the support 116 , fig3 a ). the tapered portion 120 d , since it is narrower than a base 120 e of the spring 120 b , contributes to the freedom of movement of the poppet 114 ( e . g . as in fig8 a ). fig8 a and 8b illustrate steps in the operation of a valve assembly 100 ( which has a spring 120 b , although any suitable spring may be used ). as shown in fig8 a , air under pressure has not yet been applied within the hose 132 and the and the spring 120 b urges the poppet 114 into sealing contact with the seal 169 and with the valve seat 160 . the valve assembly 100 is closed to fluid flow therethrough . fluid pressure also forces the poppet against the valve seat . on the discharge side of the valve seat at the beginning of the pumping / compression part of a cycle , the spring 120 b and the fluid within a discharge manifold pushes the poppet 114 against the seat . this continues until the pressure within the discharge manifold drops below the pressure within the pumping cylinder and / or until the actuator 130 is commanded to open . on the suction side , the fluid within the pumping cylinder pushes the poppet 114 against the seat 160 again during the compression part and until the actuator 130 is commended to open the valve . when the “ muscle ” of the actuator 130 is not expanded , there is residual air trapped between the commanding valve and the actuator 130 . the pressure of this trapped air is close to the pressure that existed in this line at the moment of exhausting the air and closing off the valve &# 39 ; s exhaust port . when the actuator is flexed , there is air at a pressure that is sufficient to open the valve , e . g . 110 psi . the actuator and air lines are filled in order to decrease the actuator &# 39 ; s response time — the time to respond to a commanding pressure . if the actuator is completely empty or , with , e . g . air at atmospheric pressure , it will take slightly longer for the actuator to respond , because when such a high pressure is applied the cavity would have to be filled with air first , then compress the air just introduced to a high enough pressure to barely stretch the hose 132 and only after that will the hose 132 change its length or respond to a commanding pressure . as shown in fig8 b , air under pressure from an air supply 200 ( with a proportional control valve 200 p ) has been applied within the hose 132 causing it to expand and pulling the cable 128 away from the valve seat 160 . in so doing , the poppet 114 is moved out of sealing contact with the seat 160 and the seal 169 of the valve seat 160 and the valve assembly is opened to fluid flow permitting fluid to flow into and out from a mud pump module housing the valve assembly . it is advantageous that the poppet is part of the valve cartridge . during assembly , when the pump is assembled for the first time , it is much easier to have a preassembled valve cartridge and , without adjustments , to insert and bolt it in and have it immediately become functional . moreover , in servicing the valve , it is much easier to extract the entire cartridge , versus bits , individual parts , and / or pieces . in certain current designs , a poppet / valve has a pseudo cartridge design in the sense that the valve has no restricting elements to keep it attached to the cartridge . in other words , the cartridge can be loosely put together prior to assembly and it can be inserted as a cartridge being secured to the body by bolts . however , if during this assembly process , or later on during servicing the valve , this cartridge is turned upside down , the valve itself can become loose and fall to the ground . often in such prior systems there is no element like a snap ring to secure the valve to the cartridge . it is also advantageous that the seal is part of the valve housing . it is easier to have the seat part of a block that can be preassembled to the pump and , later on , during a later step in manufacturing , to bolt on to it a subassembly like the valve cartridge . in designs according to the present invention , seals , e . g . the seal 169 , do not resonate . according to the present invention , such seals are surrounded by a support and have no extraneous or “ banging ” features which could be excited by a surrounding flow stream . in certain aspects according to the present invention , poppets and seats are made of ceramics which do not rust . in certain particular aspects , an alumina based ceramic offers very high strength and good wear resistance . in other aspects , a boron carbide ceramic can be used which has excellent erosion wear resistance . both of these two ceramics have a higher erosion resistance then steel . in certain aspects the poppets of assemblies according to the present invention are made with a steel core surrounded by a ceramic . the steel core supports the belleville washers and can have cut threads into it . a ceramic outer skin provides erosion resistance . in certain aspects , the special profiles facilitate the flow opening and closing the valve gradually . in certain current designs , valves have two parallel surfaces . often these surfaces form a seal that is part of conical bodies ; i . e . the seal has a conical machined surface against which is pushed a poppet . the poppet &# 39 ; s sealing surface is also conical so that , at every instance , the seat &# 39 ; s and poppet &# 39 ; s sealing surfaces are parallel . during discharge , when the two bodies are separating and , thus , allowing the fluid to flow from the pumping chamber into the discharge manifold , the fluid is squeezed in between these flat surfaces . during this phase the fluid &# 39 ; s velocity can be greatly increased as it passes from a large cross section of the pumping chamber into a small one with parallel surfaces of the valve &# 39 ; s passage way . moreover , because there is no controlling actuator , such a valve can open suddenly when the fluid &# 39 ; s pressure exerts onto the valve &# 39 ; s face a force slightly higher than that developed by the spring acting on the opposite face . as the fluid leaves at high velocity , it enters into a larger cross section that is the discharge manifold the high velocity and energy fluid acts almost like a piston in this case and pushes an adjacent block of fluid along the discharge line . this sudden move of a significant block of fluid can create a “ bang ” or a specifically loud noise almost like a pounding . this repeated banging / pounding can have detrimental effects on the drill line or other equipment . in certain valve assemblies according to the present invention , the flat parallel surfaces are replaced by curved ones . additionally , there is a controlling actuator that can open the valve before pressure in the pumping chamber reaches a value high enough to counteract the spring and , thus , to open the vale . pressure at which the fluid leaves the pumping chamber is greatly reduced . being formed in between two curved surfaces , the valve &# 39 ; s passage way flow characteristics do not impart a high velocity / energy to the fluid stream . consequently , the fluid enters and leaves the discharge manifold and line respectively in a more dispersed manner . there is no “ bang ” as in certain previous valves because the fluid does not flow in discrete “ blocks ”. the control system cs controls the air supply 200 and , thus , controls the valve assembly 100 . this is in contrast to prior valves in which fluid flow opens and closes the valve . in one aspect , the control system controls the speed with which the parts move and thereby controls the speed of opening and of closing off the valve . using appropriate software programming of programmable media in the control system , the control system controls an electro proportional valve control ( e . g . the valve 200 p , fig8 b ) that , in turn , controls the amount of air that enters or leaves the actuator 132 . consequently , the control system controls how fast , how long and how much the valve is opened . gradual opening and closing is possible which reduces pressure pulsations . each pump shaft ( crankshaft ) may have a speed sensor in communication with the control system ( e . g . a sensor 521 s , fig1 ). in systems with electric motors that drive the crankshaft ( s ), the motors are commanded through software in the control system and the same speed control signal can be broadcast to the control system . a dedicated speed sensor or a linear displacement transducer installed in every cylinder provides information for a closed loop control system ( usable , e . g ., to diagnose a pump in case of failure ). with valve assemblies according to the present invention , the valves are not connected to the crankshaft . the control system has programmable media , e . g . in a computer , computers , and / or plc ( s ). in one aspect , the control system is preloaded with a program that includes a defining equation and a curve fitter . the defining equation is a function of pump shaft speed . the curve fitter compares the curve generated by the defining equation with an “ ideal ” curve desired to drive the valve the ideal curve usually represents the valve &# 39 ; s speed , or acceleration , or opening and / or , a different relevant parameter plotted versus time . the output from the control system drives a proportional valve , a valve that controls the actuator 130 , e . g ., in one aspect , supply air into a festo ( trademark ) “ muscle ”. thus , the valve being actuated closely follows the preprogrammed curve / equation and the valve opens or closes at a certain velocity or acceleration , or that it opens at a certain rate over the duration of a pumping cycle . the opening or closing rate can be constant or variable . that is , the valve can start opening at a certain low rate followed by a higher rate followed by a different rate , and so on . in one aspect , during a cycle the valve tends to follow a certain bell - shaped curve . thus , the valve starts opening at a low rate followed at the very next instance by a slightly higher rate and in the next instance by an even higher rate and so on . all this is followed on the descending side of the curve by a lower rate followed by a slightly lower rate and so on until the valve closes . by introducing or expelling fluid into or from the pumping chamber at certain times the pump &# 39 ; s behavior is changed or the pump &# 39 ; s flow is measurable . the mechanical equivalent of controlling a valve &# 39 ; s opening rate is a cam . the cam , through its profile , controls how fast and in what relationship relative to another element , e . g . a crankshaft , the valve will open or close . in other words , it controls the valve &# 39 ; s rate ( displacement versus time ). however , a cam &# 39 ; s profile can not be changed very easily because it is cut in metal . a practical method is to introduce a hydraulically actuated push rod or cam follower in between the cam and valve . thus , the rate can change at will within a limited range . in the control strategy according to the present invention there is no piece of hardware / cam that limits the valve &# 39 ; s rate . consequently , in the proposed actuation and control strategy , the desired curve can be changed on the fly as long as the controller , e . g . a computer or plc , can accept / support it . programmability makes this equivalent to an infinitely variable profile cam shaft and the pump &# 39 ; s output flow and vibration can be controlled . ( an undesirable consequence of output flow in certain prior systems is component failure , e . g . due to cavitation .) with the curved mating sealing surfaces of the valve seat and poppet , any contact results in an effective seal . pressure fluctuations generated in or by prior art valves are reduced or eliminated and valve control reduces pressure fluctuation in the discharge line during pump operation . systems according to the present invention provide a fail safe mode . if a valve assembly according to the present invention that is inserted fails , then , for safety reasons , the pump continues working at either reduced or normal parameters until it is safe to stop it for service . in systems according to the present invention , if the actuator fails , e . g . if the muscle fails , it breaks or bursts , the valve will operate unrestricted ( e . g . as a current known design valve ). thus , the pump can continue working at almost the same parameters until it is safe to stop it . fig9 a and 9b show a valve assembly 100 a , like the valve assembly 100 ( like numerals indicate like parts ) with a spring 120 b and a poppet 114 a . the poppet 114 a has a nose 114 n projecting from a poppet body 114 b . the nose 114 n projects into the flow channel 162 of the valve seat 160 . in certain aspects , in systems according to the present invention the surface on the valve seat becomes , advantageously , more elastic . in a seal , two surfaces or edges are pushed against each other by a force . this acting force can be perpendicular to or at an arbitrary angle relative to the sealing surfaces . in systems according to the present invention the sealing bodies are the rubber seal and the poppet in one instance and , the seat itself and the poppet in a second instance . during a valve closing cycle , the first seal occurs in between a rubber o - ring and poppet . the acting force is axial relative to the poppet , but it is at an angle relative to the edge of contact between the two curved surfaces of the o - ring and poppet respectively . when the two bodies come into contact , at the point of contact , the vector components of this acting force are a normal to curved surfaces component and a tangential to curve components . this tangential component will stretch the rubber ( the over hanging part of it ) instead of purely compressing it . with the rubber o - ring being surrounded / supported by the seat &# 39 ; s rigid body , the rubber will take a very high force in compression as the normal - to - curved surfaces vector component . the rubber becomes difficult to compress when it is surrounded by a rigid wall . thus a mechanical maze is formed and , thus , the fluid encounters a high flow resistance . there is a sequence of high pressure ( inside the pumping chamber ), followed by a no flow area ( where the rubber o - ring contacts the poppet ), followed by a low pressure area ( right after the rubber seal ) and finally , followed by a no flow area at a contact between the poppet and the seat . also , the shape of the deformed rubber o - ring at the leading edge toward the impinging fluid does not allow the fluid to enter in between the poppet and seal . valve “ shivering ” occurs when a valve is not actuated ( pushed or pulled onto its seat ) with a high enough force , and flow induced forces fully or partially unseat or seat the valve in a rapid sequence . thus , the valve can not fulfill its primary function of separating two cavities . in systems according to the present invention , the actuator working against a spring reduces or eliminates valve “ shivering ” because two main forces are acting upon the valve &# 39 ; s poppet — the force generated by a compressed spring and , in opposite direction , the force developed by the festo ( trademark ) “ muscle ” or an equivalent actuator 132 . secondary forces that are pulling and pushing the poppet are those flow induced because of the high mainly axial forces generated by the two components , spring and actuator , any minute force variation induced by flow is counteracted by either one of the two large forces . the spring will oppose the motion if a minute variation will try pushing the poppet or to unseat it . conversely , the actuator will oppose any pulling or seating of the poppet ; and thus the poppet has a very stable attitude in flow . fig9 b shows the actuator 130 activated ; air applied to the hose 132 has expanded the hose 132 making it contract down , thereby , unseating the poppet 114 a from the valve seat 160 . a valve assembly according to the present invention with a poppet like the poppet 114 a provides uniform and stable poppet positioning and movement . fig9 d illustrates a velocity profile of incoming fluid e flowing around a poppet 114 a . two rings a of high velocity fluid flow surround the poppet 114 a . the rings a are continuously and uniformly distributed all around the poppet 114 a , creating elastic cushions b that surround and stabilize the poppet 114 a , e . g . in the event of a disturbing force acting in a direction other than in an axial direction . a reverse fluid flow c ( part of the flow e which has changed direction ) acting on a back side of the poppet 114 a tends to push the poppet 114 a into the closed position shown against the incoming flow e and against the two elastic cushions b . the uniformity and distribution of the flow c also facilitate the maintenance of the poppet 114 a in a stable attitude . fig9 e illustrates pressure distribution of an incoming flow e around the poppet 114 a . high pressure elastic fluid cushions d that surround and stabilize the poppet 114 a . the incoming flow e has a smooth transition around the nose 114 m of the poppet 114 a and the ensuing flow sticks ( binds to or tends to flow along adjacent a curved surface ) to the curved poppet surfaces . a reverse flow c will not suffer a sudden change in direction , but a gradual one ( e . g . as illustrated by the curved arrows w of the flow c at the back of the poppet ). in certain prior valves such a flow hits a poppet &# 39 ; s back surface and flows at or near a ninety degree angle to the back of the poppet . wobbling of the poppet 114 a is reduced or eliminated and it will maintain a stable position with its vertical axis concentric with that of the tubular within which it is positioned . in contrast , in certain prior art valve assemblies with typical plain rounded - head poppets , there are sudden ninety degree changes of fluid flow direction on both faces of the poppets . sudden changes in the direction of fluid flow , as well as turbulence behind the poppet , can generate some flow - induced destabilizing forces . also , with such typical plain rounded - head poppets with relatively large flat end surfaces , two areas of low pressure ( vacuum or close to vacuum ) are developed around sharp edges of the poppets . these areas are within and surrounded by high pressure . this pressure distribution can lead to cavitation and unstable attitude in flow . also , discrete veins of flow can occur where these low pressure areas take place . consequently , because of a non - uniform distribution around the body , the poppets will have a precession motion . this effect is amplified by the geometrical dimensions of the poppets . non - uniform flow distribution results on the poppets back sides . fig1 a - 10d illustrate a poppet 114 b on a base 114 s on a spring 120 c ( see also fig1 ) according to the present invention . the spring 120 c has an end 120 g with projections 120 k . optionally , there are one or three projections 120 e the projections 120 k have curved portions 120 m which enhance freedom of movement of the poppet 114 b so it can be self - centering . it is within the scope of the present invention to at least one , one , two , or more projections 120 k . a pin 120 f rests in a recess 120 r of a support 120 h . the pin 120 f projects through openings in the projections 120 k to secure the spring 120 c to the support 120 h . a cable ( not shown ) is wrapped around ( or connected to ) the pin 120 f and extends down through the spring 120 c . a hole 120 u houses a set screw 120 w to secure the base 114 s to support 120 h . in certain particular aspects , two first coils 120 j of the spring 120 c , optionally of high elasticity material allow the poppet 114 b to center itself on a seat . after seating of the poppet 114 b against a seat , the coils 120 j are completely compressed and in contact . the remaining coils of the spring 120 c take the load and thus elastically support the poppet 114 b . the support 120 h ( see , e . g ., fig1 a - 12c ) has a base 120 m with two holes 120 z for the spring projections 120 k . the present invention , therefore , provides in at least some embodiments , a system for pumping a drilling fluid mixture , the drilling fluid mixture containing drilling fluid and solids , the system including : a pump apparatus ; the pumping apparatus having a body with an inlet and an outlet ; a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet ; a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet ; each of the suction valve and the discharge valve having a seat with a curved valve seat surface and a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat . such a system according to the present invention may have one or some ( in any possible combination ) of the following : a seal recess in the curved valve seat of each of the suction valve and the discharge valve , a seal positioned in each seal recess so that resonating of the seal is inhibited , each valve member movable to seat against a corresponding seal ; wherein each valve member has a range of freedom of movement for effecting seating against an adjacent corresponding curved valve seat surface ( and , in certain aspects , against a seal in the valve seat ), the freedom of movement including the ability to move not just toward and away from the vavle seat but at an angle thereto ; wherein each valve member has a spring urging the valve member against the curved valve seat surface ; wherein the spring has a spring body with a first end and a second end , the first end in contact with the valve member , the first end tapering from the spring body ; each valve having a cartridge stem positioned with respect to the valve member , and a valve actuator within the cartridge stem for selectively moving the valve member ; wherein the valve actuator is interconnected with the valve member via a cable ; the valve actuator includes a selectively expandable hose for moving the valve member ; an air supply for supplying air to the valve actuator , and a control system for controlling the air supply to selectively open and close the valve ; a ball movably mounted within each valve member , the cable connected to the ball and to the valve actuator , the valve member movable with respect to the ball ; each valve member has a rounded nose and a curved tapered outer surface so that fluid flow contacting the nose and curved tapered outer surface forms stabilizing fluid cushions around the valve member ; each valve member has a back surface , a portion of the fluid flow onto the nose and curved outer surface gradually changes direction on the back surface ; wherein the seat has a flow channel adjacent the curved valve seat and the valve member is movable to close off flow through the flow channel and wherein the flow channel is unobstructed ; and / or wherein each valve member has a spring urging the valve member against the curved valve seat surface , each spring having a top end with at least one curved spring projection , a spring mount within the valve member , the at least one spring projection movably connected to the spring mount to facilitate freedom of movement of the valve member with respect to the curved valve seat surface and / or a dampener within the body for inhibiting pulsations of fluid pumped from the pump apparatus . the present invention provides systems for pumping a drilling fluid mixture , the drilling fluid mixture containing drilling fluid and solids , the systems having : a pump apparatus , the pumping apparatus having a body with an inlet and an outlet , a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet , a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet , each of the suction valve and the discharge valve having a seat with a curved valve seat surface and a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat , a seal recess in the curved valve seat surface of each of the suction valve and the discharge valve , a seal positioned in each seal recess so that resonating of the seal is inhibited , each valve member movable to seat against a corresponding seal , each valve having a cartridge stem positioned with respect to the valve member , and a valve actuator within the cartridge stem for selectively moving the valve member . the present invention provides a method method for pumping fluid , the method including : sucking fluid into an inlet of a pumping apparatus of a system , the system comprising a pump apparatus , the pumping apparatus having a body with an inlet and an outlet , a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet , a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet , each of the suction valve and the discharge valve having a curved valve seat surface and a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat ; and with the pump apparatus , pumping fluid into the inlet and then out the outlet . the present invention provides wherein such a system , in certain aspects , that has a seal recess in the curved valve seat of each of the suction valve and the discharge valve , a seal positioned in each seal recess so that resonating of the seal is inhibited , each valve member movable to seat against a corresponding seal , the method further including seating each valve member surface agains a corresponding seal ; and / or wherein each valve has a cartridge stem positioned with respect to the valve member , and each valve has a valve actuator within the cartridge stem for selectively moving the valve member , the method further including actuating each of the suction valve and the discharge valve with the valve actuator . the present invention provides a method for pumping fluid , the method including : sucking fluid into an inlet of a pumping apparatus of a system , the system having a pump apparatus , the pumping apparatus having a body with an inlet and an outlet , a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet , a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet , each of the suction valve and the discharge valve having a curved valve seat surface and a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat , wherein each valve member has a range of freedom of movement for effecting seating against an adjacent corresponding curved valve seat surface ; with the pump apparatus , pumping fluid into the inlet and then out the outlet ; controlling fluid flow in through the inlet with the suction valve ; and controlling fluid flow out the outlet with the discharge valve . the present invention provides a method for pumping fluid , the method including : sucking fluid into an inlet of a pumping apparatus of a system , the system including a pump apparatus , the pumping apparatus having a body with an inlet and an outlet , a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet , a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet , each of the suction valve and the discharge valve having a curved valve seat surface and a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat , each valve having a cartridge stem positioned with respect to the valve member , and a valve actuator within the cartridge stem for selectively moving the valve member ; with the pump apparatus , pumping fluid into the inlet and then out the outlet ; and with the valve actuator selectively operating the suction valve and the discharge valve . the present invention provides a valve for a valve assembly for a pump apparatus of a system for pumping a drilling fluid mixture , the drilling fluid mixture containing drilling fluid and solids , the pumping apparatus having a body with an inlet and an outlet , the valve for disposition in one of the inlet and outlet for selectively controlling flow of the drilling fluid mixture , the valve including : a seat with a curved valve seat surface , a valve member with a curved member surface , part of the valve member movable to seat the curved member surface against the curved valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat . such a valve may have a seal recess in the curved valve seat surface , a seal positioned in the seal recess , the valve member movable to seat against the seal . the present invention provides a valve for a system for pumping a drilling fluid mixture , the drilling fluid mixture containing drilling fluid and solids , the valve having : a seat with a valve seat surface , a valve member with a member surface , part of the valve member movable to seat the member surface against the valve seat surface to prevent the flow of the drilling fluid mixture past the valve seat , a cartridge stem positioned with respect to the valve member , and a valve actuator within the cartridge stem for selectively moving the valve member . the present invention provides system for pumping a drilling fluid mixture , the drilling fluid mixture containing drilling fluid and solids , the system having : a pump apparatus , the pumping apparatus having a body with an inlet and an outlet , a suction valve in the body for selectively controlling flow of the drilling fluid mixture in through the inlet , a discharge valve in the body for selectively controlling flow of the drilling fluid mixture out through the outlet , and a dampener within the body for inhibiting pulsations of fluid pumped from the pump apparatus in conclusion , therefore , it is seen that the present invention is well adapted to carry out the objectives and obtain the ends set forth . certain changes can be made in the subject matter without departing from the spirit and the scope of this invention and changes are possible within the scope of this invention and it is further intended that each element or step recited herein refers to the step literally and / or to all equivalent elements or steps . this specification is intended to cover the invention as broadly as legally possible in whatever form it may be utilized . all patents and applications identified herein are incorporated fully herein for all purposes .