a chair with a backrest adjustable in angle as in the present invention , is shown in fig1 & amp ; 3 , and comprises a bottom supporter 1 , a base plate 2 , a seat 3 , and a backrest 4 as the main components . the bottom supporter 1 includes a plurality of casters 11 for the chair to move freely on the ground , an air pressure cylinder 12 vertically provided at the center , a press button 13 to actuate the cylinder 12 to adjust the height of the seat 3 , a u - shaped plate 14 provided at the top having two opposite vertical sides respectively bored with two holes 141 for rotatable pins 143 to insert in for attaching an intermediate plate 15 , which can pivot - somewhat with the pins 143 as a center , and two holes 142 , 142 &# 39 ; for a control rod 16 to pass through and be inserted in the holes 152 , 152 &# 39 ; in the intermediate plate 15 to hold the plate 15 immovable . the intermediate plate 15 has a side hole 151 for a rotatable pin 143 to attach the plate 15 on the u - shaped plate 14 , and the side holes 152 , 152 &# 39 ; for the control rod 16 to pass through . the plate 15 cannot pivot when the control rod 16 passes through both the holes 142 , 142 &# 39 ; and 152 , 152 &# 39 ;, but the plate 15 can pivot somewhat when the control rod 16 is withdrawn from holes 142 &# 39 ; and 152 &# 39 ;. the control rod 16 can rotate while located in the holes 142 , 142 &# 39 ;, 152 , & amp ; 152 &# 39 ;, causing a protrusion 161 provided near its end to push down on the press button 13 to actuate the air pressure cylinder 12 . the plate 15 also has a hole 153 for a bolt 154 to pass through vertically to combine with a ring 155 , a coiled spring 156 and a cap 157 to provide the chair with a rocking function . the plate 2 is positioned under the seat 3 , combined together with the intermediate plate 15 as an unit , and having an upright wall 21 bored with a hole 22 for a bolt 221 to pass through and thread onto a nut 22 to attach an elongate plate 231 of an elastic assembly 23 with the wall 21 . the plate 231 has two holes 232 for receiving two bolts 233 to thread with two nuts and mount coiled springs 234 having one of their ends resting on the plate 231 and the other of their ends formed into annular hooks for a bolt 235 to pass through to connect the springs with a connecting plate 236 which has an end tubular hole for the bolt 235 and pass through to screw with a nut 237 . the connecting plate 236 has another tubular hole at the opposite end for a bolt 238 to pass through to connect the plate 236 with a u - shaped connector 43 of the backrest 4 . the elastic assembly 23 includes the connecting plate 236 , the elongate plate 231 , the two coiled springs 234 , bolts 233 , 235 and nuts combined to pull back automatically the backrest with the elasticity of the springs 234 . the seat 3 is combined with the plate 2 at its bottom , and two u - shaped armrests 31 are attached by means of bolts 32 , and nuts 33 at both sides of the seat 3 , as is well - known in the art . the seat 3 can be padded with foam rubber or the like to make it comfortable for sitting on . the backrest 4 has two holes 41 at the bottom to connect a limit plate 42 with the backrest 4 , and the limit plate 42 is connected with u - shaped connector 43 linked to one end of the connecting plate 236 . therefore , after the backrest 4 is pushed backward , it can be automatically pulled back to its original position by the elasticity of the two coiled springs 234 . the limit plate 42 has two side holes 421 for two bolts 24 to pass through to combine the limit plate 42 with the plate 2 through bolts 24 to pass through holes 25 , and the limit plate 42 is kept positioned inside both side walls of the plate base 2 and can be inclined through a limited angle with the bolts 24 as pivots , with two protrusions 26 provided in the plate base 2 forming stops . the limit plate 42 also has a tube 422 for the end of a steering rod 27 to fit in for keeping the limit plate 42 and the backrest 4 immovable . the steering rod 27 passes through two holes 281 in a u - shaped bracket 28 fixed on the plate 2 , and has two position pins 271 provided crosswise and spaced apart a certain distance so that one of the pins 271 can be arrested by one of the bent side walls of the u - shaped bracket 28 limiting the movement of the steering rod 27 to a certain distance . next , referring to fig2 & amp ; 3 , when the steering rod 27 is moved insert into the shaft tube 422 , the backrest 4 is kept upright and immovable as shown in fig3 . when the steering rod 27 is pulled out of the shaft tube 422 as shown in dotted lines in fig2 & amp ; 3 , the backrest 4 can be inclined backward , and kept in its inclined position by the position protrusions 26 in the plate base 2 touching and stopping the limit plate 42 . fig4 shows that when the protrusion 161 on the control rod 16 is not pushing down the press button 13 , the air pressure cylinder 12 cannot function to move up or down the seat 3 . but when the control rod 16 is rotated , as shown in fig5 to make the protrusion 161 face down and push down on the press button 13 , the air pressure cylinder 12 can function to move up or down the seat 3 . in short , the backrest 4 can be adjusted to an upright or tilted position by means of the steering rod 27 , and the seat 3 can be adjusted in height by means of the control rod 16 .
a chair with its backrest adjustable in its angle comprising a steering rod to keep the backrest upright or tilted in a certain pre - set angle and a control rod to push down a press button of an air pressure cylinder which functions to raise up or lower down the seat of the chair when the control rod is rotated .