Reciprocating pump is a class of positive displacement pump which includes piston pump, plunger pump, and diaphragm pump. It is often used where a relatively small quantity of liquid to be handled and where delivery pressure is quite large. Priming is not required because it is positive displacement pump. Reciprocating pumps have lower efficiency compared to centrifugal pump.
API 674 – Positive Displacement Pump – Reciprocating covers minimum requirements for reciprocating positive displacement pumps for refinery application. The standard also covers piping and instrumentation required for the pump.
API 674 stated that in general piping system for reciprocating pump shall:
- Include all necessary piping, isolation valves, control valves, relief valves, pressure reducers, restriction orifices, thermometers, and all vents and drains.
- Be fabricated preferably by bending and welding to minimize the use of flanges and fittings. Threaded connections shall be held to a minimum. Pipe bushings and closed nipples shall not be used.
Pulsation Suppression Device
Since flow from reciprocating pump is not uniform, disturbance (pulsations) are created. It is created due to oscillating motion of the plungers that travel at the speed of sound from pump cylinder to the piping system. Pulsations cause the pressure level of the system fluctuate with respect to time.
Pulsation at suction pump can cause the pressure level to drop instantaneously below the vapor pressure of fluid which results in cavitation. Cavitation can cause failure in pump parts and high piping vibration which leads to failure of vents, drains, and gauge. To solve this problem pulsation dampener is installed at suction and discharge of pump to attenuate the effect of pulsation flows.
Typical Piping and Instrumentation Diagram for Reciprocating Pump
Figure below is typical piping and instrumentation diagram for reciprocating pump.
In the above picture, there are several main components of P&ID reciprocating pump.
- Class break, to differentiate piping class before entering the system and after entering the system. Because the pressure at upstream of the pump is low, so #150 is enough. In this case I assume class break #150/#1500
- Block valve at suction and discharge of pump. In this case I use double block and bleed due to high pressure of pump
- Strainer at suction pump to remove dirt from liquid
- Pressure gauge at suction pump to monitor liquid pressure before pumping
- Pulsation dampener at suction and discharge pump to minimize pulsation
- Pressure gauge at discharge pump to monitor liquid pressure after pumping
- Check valve to avoid back flow
- Pressure safety valve to avoid liquid pressure exceed maximum allowable working pressure.
- Control valve to control pressure of liquid after pumping
About pressure safety valve, API 674 stated several requirements.
- Relief valve shall be set to relieve fully at not more than maximum allowable working pressure but at not less than 110% of the rated discharge pressure or 25 psig, whichever is higher.
- Relief valve must be able to handle the pump rated capacity when fully open, at a pressure not more than 10% above the set pressure.