Circulating pump for high pressure and high temperature applications
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;tee” fitting and thence to a pair of check valves and 1/4 in. o.d. flow lines as indicated in Fig. 1. The four check valves served to rectify the flow to the desired direction during both forward and reverse strokes of the piston. The springs in the check valves were removed to reduce the cracking pressure required to open them. To ensure the most efficient operation, the pump was orientated such that the check valves were aligned roughly vertically, with the flow in the upward direction, so that the closure occurred by gravity. Nevertheless, deviations of at least ±30° from verticality were found to be acceptable, and the desired mobility of the pump was not compromised.
The pump drive was, by means of a pneumatically activated piston cylinder, operated in conjunction with a process controller, solenoid valves, and air flow _speed_ and pressure _force_ regulators. The pneumatic cylinder was linked to the magnet assembly and carrier plate by means of a push rod. The carrier plate to which the magnet assembly was fixed was free to slide on a pair of linear rotary ball shafts to which a high-temperature grease _Ondrive Ltd., UK, product CG2- SY_ has been applied, thereby providing high precision and smoothness to the linear reciprocating action of the pump. A pair of microswitches was used to sense the end-of-travel conditions and thence to reverse the action of the pneumatic cylinder by the operation of the solenoid valves controlling the air flow. In this way, the piston travel was adjusted to be 6 cm in each direction, leading to a theoretical displacement of 6 cm3 per cycle. The process controller permitted a speed variation during the cylinder operation; it could also be interfaced to a computer for integration into an overall control System. 
Circulating pump for high pressure and high temperature applications
III. OPERATION AND PERFORMANCE
The reciprocation of the piston creates flow in the cylinder, with the fluid drawn in behind the piston and pushed out in front. The check valves ensure that the overall flow is unidirectional and nearly continuous.
The pump has been tested successfully in a high pressure and high-temperature operation. Performance tests were also conducted at 25 °C with a liquid feed at ambient pressure. During these tests, the outlet from the pump was fitted with a pulsation dampener comprising a vessel of 100 ml volume that was initially filled with ambient air and then connected at its lower end to the liquid flow line. The outflow passed through a needle valve