The present invention relates to a method and apparatus for pumping compressible materials using a twin-cylinder, reciprocating piston pump. More specifically, the present invention relates to a hydraulic system for operating a reciprocating piston pump that includes an accumulator that produces a steady-pressure supply of compressible material to an application nozzle and has a device for compensating for the varying demands of the material being pumped and the job site being worked.
Fire proofing material is one example of a compressible material that is commercially pumped using a twin-cylinder, reciprocating piston pump. In a typical reciprocating piston pump, while one cylinder is drawing material from a holding hopper, the other cylinder is pushing the material out into a delivery line that eventually terminates, at a distribution nozzle. At the distribution nozzle, the material is sprayed with the assistance of a supply of compressed air.
As mentioned above, in twin-cylinder, reciprocating piston pumps, when the two pistons are near the end of their cycle, the pistons switch modes. For example, the first piston goes from the pumping mode to the material drawing mode, while the second piston goes from the material drawing mode to the pumping mode. During this transition, there is a decrease in the delivery line pressure. This decreased line pressure continues until the pumping cylinder reaches its operator-designated speed. The fluctuation in pumping pressure during the transition between the cylinders has the effect of creating a non-continuous flow through the distribution nozzle. This non-continuous flow is referred to as line surge, which is highly undesirable for the nozzle operator. Specifically, line surge can cause muscle fatigue in the nozzle operator and creates a loss of efficiency in the pumping system.
Line surge is amplified in vertical pumping of the compressible material due to the force of gravity. For example, when compressible material is pumped upward, gravity pulls the material back toward the pumping apparatus and away from the distribution nozzle. The amplification of the line surge is proportional to the vertical distance the material is being pumped.
In addition to the effect of gravity, when pumping compressible material, an additional factor affects the line surge. Specifically, the line surge is affected by the springy nature of the material being pumped, since the efforts to push the material through the initial stages of the delivery hose are dampened. The pumping force is dampened because the compressible material has a tendency to push back toward the pumping apparatus if the pressure is not kept constant. Furthermore, the design of the hydraulic system may not be optimized for the material, since the level of compressibility varies with the material being pumped. Currently, numerous types of compressible materials exist in today""s market place.
Currently, material line surges are decreased by adding a pre-charged, gas-assisted accumulator into the hydraulic system for the reciprocating piston pump. When the hydraulic line pressure to the piston pump drops below the pre-charged accumulator pressure, the accumulator""s volume of oil is released into the system to provide a xe2x80x9cturboxe2x80x9d boost to the pump. When the hydraulic line pressure from the source pump ramps up to a pressure above the accumulator pressure, normal pumping resumes and the accumulator bladder is refilled.
Presently, the size and volume of the accumulator are selected such that the accumulator will decrease or eliminate the line surge at a specified set of job site conditions. Typically, the accumulator is selected based upon a worst-case scenario of long-distance vertical pumping, such as the top of a high rise building. Because of this bias toward a single operating condition, the pumping system has a predisposition toward increased line surges when pumping in other conditions different than the preset value.
In order to compensate for the preset site selection of the accumulator volume, pump operators compensate in one of two ways: 1) decrease the volume of material being pumped to less than the machine""s full capacity or 2) run the material through extra lengths of coiled delivery line to simulate the long distance pumping environment. Although these two methods of operation reduce line surge, both of these adjustments increase capital costs, decrease efficiency and increase setup and cleanup times.
Therefore, it is an object of the present invention to provide a method and apparatus for pumping compressible materials that have varying degrees of compressibility, over infinitely-varying horizontal and vertical distances within the expected pumping capabilities of the apparatus. Further, it is an object of the present invention to provide such an apparatus and arrangement that utilizes a minimum number of components, thereby making the system cost-effective to manufacture, maintain and operate. Further, it is an object of the present invention to provide such an apparatus that will eliminate the need for the operator to take extraneous means or methods to control line surge at the distribution nozzle.
The present invention relates to a hydraulic system, including an accumulator, that produces a steady supply of compressible material to a distribution nozzle. Specifically, the present invention relates to a hydraulic system for use with a twin-cylinder, reciprocating piston pump that includes means for constricting the output of an accumulator to adjust for varying demands of the material being pumped and the job site being worked.
The hydraulic system of the present invention includes an accumulator that is positioned in the supply line leading from the hydraulic fluid pump to a control valve that directs the flow of hydraulic fluid to a pair of cylinders of the reciprocating piston pump. The accumulator includes means for constricting the flow of the stored hydraulic fluid from the accumulator to the pair of cylinders through the control valve. Specifically, the accumulator includes a needle valve that allows the operator to constrict the flow of hydraulic fluid from the accumulator based upon the material being pumped and the job site being worked. For example, the output flow of the accumulator can be restricted based upon the distance and height that the material is being pumped, as well as based upon the compressibility of the specific material being pumped.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.