How does the pump head work of the reciprocating compressor?

Pump head technology

The purpose of the pump head is to convert power from the drive into hydraulic power, which corresponds to an increase in fluid flow and pressure. 

In the case of plunger pump heads, the reciprocating plunger acts directly on the pumped fluid as a displacer. The plunger discharges the fluid out of the pump body and then sucks it back in.

Plunger pump

A step-by-step approach has proven useful for describing the function of metering pump heads and for understanding the basic mechanisms. Reasons and explanations are given for technical solutions ranging from simple to complex along the "evolutionary line of metering pump heads".

Work cycle/pressure course in the pump head

The work cycle of the plunger pump head is illustrated in figure1. The discharge stroke of the plunger begins at the rear dead center (RDC) with the relatively brief compression phase (1-2), since all fluids exhibit compressibility, even if it is generally low. When the fluid is compressed to the discharge pressure, the pressure valve opens. The flow phase then takes place and the fluid is discharged into the discharge line (2-3). After reaching the front dead center (FDC), the decompression phase begins (3-4), followed by the suction phase from the suction line into the pump head (4-1).

The indicator diagram shows the pressure course in the pump head as a cycle. The pressure course is also depicted over time. The nearly sinusoidal plunger travel between RDC and FDC is also shown in relation to time, as well as the plunger velocity as its derivative. Multiplying the plunger velocity by the constant plunger area yields the flow rate. It is then easy to see that the velocity and the flow rate are equal to zero at the RDC and the FDC and change direction. They reach their maximum values at the crank angle of 90° or 270°. In the following designs, the functional principle of a plunger pump is examined in more detail. 

In order to show why and how the plunger pump was developed into the diaphragm pump, its advantages and disadvantages must be taken into consideration.

Primary advantages of the simple plunger pump: 

– Low part count, cost-effective 

– High efficiency 

– High discharge pressure 

– Precise metering 

– Simple handling and repairs 

Primary disadvantages of the simple plunger pump: 

– The plunger seal is wetted and can be damaged by aggressive fluids or solids 

– The plunger seal and plunger can experience wear, which leads to contamination and higher maintenance costs 

– The plunger and gasket are therefore often very specific and made of expensive materials

– Plunger pumps always leak into their surroundings or the flushing system 

The task now is to maintain the advantages of plunger pumps and make design changes to eliminate the disadvantages step by step.