Triplex Piston Pump

Introduction

This is a 3D model of a Triplex Piston Pump.

3D Model Annotations

Triplex Piston Pump

A triplex piston pump is a reciprocating positive displacement pump that uses only three pistons. This type of pump is often used for high pressure applications e.g. hydraulic systems. Due to its robust design, it is capable of pumping high viscosity fluids and fluids which contain solids.

Piston

Fluid is drawn into a cylinder, or discharged from a cylinder, by its associated piston. When a piston is closest to the suction and discharge valves, it begins to move in a linear direction back towards the crankshaft. As it retracts, the negative pressure within the cylinder overcomes the suction valve spring pressure, and fluid is drawn into the cylinder space; this movement represents the ‘suction stroke’. When the cylinder is fully charged, the piston moves linearly back towards the suction and discharge valves. As the piston moves towards the valves, the positive pressure within the cylinder causes the suction valve to close and the discharge valve to open; fluid is then discharged from the cylinder through the discharge valve.

Suction Valve

The suction and discharge valves are non-return valves; the valve highlighted by this annotation is the suction valve. Flow through non-return valves can only occur in one direction. For the suction valve, a negative cylinder pressure causes it to open, whilst a positive pressure causes it to close. For the discharge valve, a negative pressure causes it to close, whilst a positive pressure causes it to open. The pressure at which each valve opens and closes (cracking pressure) is dictated by the residual stress present in the valve springs (a stiffer spring requires a larger pressure to open).

Discharge Valve

The suction and discharge valves are non-return valves; the valve highlighted by this annotation is the discharge valve. Flow through non-return valves can only occur in one direction. For the suction valve, a negative cylinder pressure causes it to open, whilst a positive pressure causes it to close. For the discharge valve, a negative pressure causes it to close, whilst a positive pressure causes it to open. The pressure at which each valve opens and closes (cracking pressure) is dictated by the residual stress present in the valve springs (a stiffer spring requires a larger pressure to open).

Crankshaft

An eccentric shaft (crankshaft) offsets the rotating position of each of the triplex pump pistons. The offset amount is what gives each piston its stroke length e.g. 5 cm offset from the shaft centre axis of rotation would yield a 5 cm suction or discharge stroke. The shape of the shaft dictates the position of the piston within the cylinder. Each of the crankshaft webs is offset by 120 degrees, which means that each piston is leading or lagging the other pistons by 120 degrees (suction stroke positions differ, discharge stroke positions differ). Varying the discharge and suction strokes of each piston reduces pump vibration and reduces the load on the pump components and driver (less energy is required to discharge one piston than three pistons simultaneously).

Drive Shaft

The power to rotate the pump is provided via the drive shaft. Triplex piston pumps are usually electrically or mechanically driven, although it is also possible to hydraulically operate the pump. The entire load is transmitted through the drive shaft, thus the shaft has a correspondingly large diameter.

Pressure Gauge

A pressure gauge is used to give operators a visual indication of the internal lubrication oil pressure. The type of gauge used for this application is usually a bourdon gauge.

Oil Filter

An oil filter (or oil filters) remove foreign bodies from the lubrication oil. Foreign bodies are typically items such as metal shavings, dirt, and dust. ‘Dirty’ oil is taken from the triplex pump sump (inside the casing) and passed through the oil filter; 'clean' oil is discharged from the filter and enters the triplex pump casing.

Oil Pressure Regulator

An oil pressure regulator is used to regulate the pressure delivered to the oil filter.

Casing

The casing houses the eccentric shaft (crankshaft), pistons, cylinders and bearings.

Pressure Differential Switch

Pump alarms and shutdowns are triggered by signals received from the lubrication oil pressure differential switch. Should the lubrication oil pressure operate outside of normal operating parameters e.g. low oil pressure, or low low oil pressure, the differential pressure switch will send a signal to alarm or shutdown the pump. The differential pressure switch is thus a type of protection device and must be maintained accordingly.

Oil Pump

Lubrication oil is drawn from the triplex pump sump and discharged to the oil filter via a pressure regulator. The pump is driven by the main pump shaft; its speed (and the volume pumped) is thus proportional to the shaft speed.

Discharge

High pressure fluid is discharged through this connection.

Suction

Low pressure fluid is drawn into the pump through this connection.

Encyclopedia - saVRee