High-pressure pumps are at the heart of almost every application that moves fluids reliably at high pressure. CAT PUMPS builds them as triplex, positive-displacement reciprocating pumps – in three designs that differ in valve actuation and sealing concept, and therefore in their strengths.
Piston pump – “Uniflow” design
The piston pump is designed for the fluid to move continually in one smooth forward direction. This allows greater suction capability and reduces the risk of cavitation, provided the pump is properly primed.
At the beginning of the stroke, the mechanically actuated inlet valve closes. As the piston rod moves forward, liquid is forced out through the discharge valves; at the same time, liquid enters the pump inlet and collects behind the inlet valve. On the backward stroke the inlet valve opens mechanically, letting the liquid continue forward through the piston into the discharge chamber until the stroke is complete.
Plunger pump – “Direct Flow” design
The spring-reinforced, preset packing design of the plunger pumps permits significantly greater pressures than piston pumps. They also offer considerable versatility: optional direct coupling drives and a wide range of wet-end material options.
As with the piston pump the liquid flows forward, but here both valves are spring-loaded closed and hydraulically opened. At the beginning of the stroke the plunger displaces the liquid in the manifold chamber and forces the discharge valve open. There is a split second at the end of the stroke when both valves are closed. As the plunger rod begins its backward stroke, the inlet valve opens to admit more liquid into the manifold chamber, keeping the flow smooth.
SF plunger pump – “Superflow” design
In the SF series both inlet and discharge valves are spring-loaded closed and hydraulically opened as in the plunger pumps, but the ceramic plunger is ported. The design therefore combines the continuous forward flow of the piston pump with the packing concept of the plunger pump: strong suction capability together with higher pressure performance.
At the beginning of the stroke the inlet valve closes against the ceramic plunger and the flow is forced out through the discharge valves. On the backward stroke the inlet valve moves away from the plunger, and liquid flows through the holes in the ceramic plunger into the manifold chamber.
Note for all three designs: The spring tension on the discharge valves requires a minimum discharge pressure of 7 bar (100 psi) for the valves to operate properly.
Our product range shows the available series; the pump finder leads straight to a suitable model.
How does a CAT PUMPS high-pressure pump work?
They are triplex, positive-displacement, reciprocating pumps. Each revolution of the crankshaft creates a direct motion in the plunger or piston rods, producing a positive output of flow. Bore and stroke determine the amount of liquid handled per stroke and revolution, and the flow is in direct relation to pump speed. Pressure is not created in the pump but by the restriction downstream – the nozzle, for instance.
What is a plunger pump and how does it work?
A plunger pump is a reciprocating positive-displacement pump. A ceramic-coated plunger moves back and forth inside a pumping chamber: on the suction stroke, fluid is drawn in through the inlet valve; on the pressure stroke, it is discharged through the outlet valve at high pressure. Because the same volume is displaced with every revolution, the pump delivers an almost constant flow rate – independent of back pressure.
How do piston and plunger pumps differ?
In the piston pump the inlet valve is mechanically actuated and the seal travels with the piston, which gives greater suction capability and a lower tendency to cavitate. The plunger pump uses spring-loaded, hydraulically opened valves and stationary, spring-reinforced packings – allowing significantly higher pressures, direct coupling drives and a wider choice of wetted materials.
How does a plunger pump differ from a centrifugal pump?
A centrifugal pump generates pressure through the flow velocity of an impeller, so its flow rate drops as back pressure rises. A plunger pump displaces a fixed volume per stroke and therefore reaches very high pressures of several hundred bar at constant flow and high efficiency. For high-pressure applications from roughly 50 to 100 bar upwards, the plunger pump is the right choice.
Why do most CAT PUMPS pumps have three plungers (triplex design)?
Three plungers offset by 120° balance each other's delivery. The result is a smooth flow with low residual pulsation, quiet running and long service life for seals and valves.
What determines the flow rate of a high-pressure pump?
Displacement volume and speed alone – not pressure. Halving the speed halves the flow rate. This is exactly how flow is set within a system: through pulley ratios or, continuously, via a variable-frequency drive. The choice of motor also plays a part: its number of poles determines the speed, and 4-, 6- or 8-pole designs are common.
Why do the discharge valves need a minimum pressure?
The discharge valves are spring-loaded. To open and close properly they require a discharge pressure of at least 7 bar (100 psi). Below that the valves do not work reliably, so the system should never be run at near-zero pressure for extended periods.
Which applications use high-pressure pumps?
Typical fields are high-pressure cleaning, water-jet deburring, pressure testing, reverse osmosis, spray cooling and humidification, fire protection with water mist, transfer of demineralised water and chemicals, and industrial process technology.