A Guide to the Different High-Pressure Pump Mechanisms

At its core, a high-pressure pump is an equipment that moves or transports a medium, in the process intensifying its flow rate and pressure.

Mediums and high-pressure pump applications vary. Water is a typical medium. High-pressure water jetting systems intensify water pressure for abrasive cold cutting, hydrostatic testing, and hydroblasting applications, such as drill pipe and sewer cleaning, surface preparation, tank and vessel cleaning, and tube cleaning.

There are many types of high pressure pumps, varying mainly in their pumping mechanism. However, there are two main categories of high pressure pumps: centrifugal pumps and positive displacement pumps.

Centrifugal Pumps

Centrifugal pumps work by using centrifugal force to move the medium radially outward at high speeds, while the pump casing slows down the medium, converting medium velocity to pressure.

In a centrifugal pump, the medium or fluid enters through the eye of the pump. The impeller moves at high speed, transferring rotational kinetic energy to the medium. Consequently, the medium is cast out to the circumference of the impeller vanes and onto the pump casing.

The pump casing converts the medium’s velocity to pressure, intensifying the pressure as the medium exits through the discharge valve.

Types of Impeller Assemblies

An impeller is the part of the pump that moves the medium in a centrifugal pump. There are three main types of impeller assemblies depending on whether the impeller has a metal shroud.

● Open Impeller

The impeller is open at the front and the back. This type of impeller assembly is not very efficient as the medium in the vanes can freely interact with the medium in the casing.

● Semi-Open or Semi-Enclosed Impeller

This impeller is attached to a plate at the back. Structurally more robust than the open impeller type, the semi-open impeller is still not the most efficient.

● Closed Impeller

A plate or a metal shroud encloses the impeller vane at the front and the back. This shroud separates the medium inside the impeller vanes from the high-pressure medium in the casing. Thus, this type of impeller assembly is the most efficient. It is also the strongest.

Types of Casings

The pump casing is the housing that encloses the impeller and contains the medium before it gets to the discharge valve. There are two main types of centrifugal pump casings: volute and diffuser.

● Volute Casing

In a centrifugal pump with a volute casing, the impeller assembly is offset from the center. The casing area increases as it nears the discharge valve.

This design allows the medium to build up in the casing, slowing the medium down and allowing for higher pressure buildup.

The volute casing is appropriate for applications involving mixed and higher-viscosity mediums.

● Diffuser Casing

In the diffuser design, the impeller assembly is at the center of the pump. There are diffuser vanes at equidistant intervals all along the circumference of the impeller to aid in pressure buildup.

This type of casing is better suited to homogenous and lower-viscosity mediums.

Types of Centrifugal Pumps by Number of Stages

● Single Stage Pump

Single stage centrifugal pumps have only one impeller assembly.

● Two Stage Pump

A two stage pump, as the name suggests, has two impeller assemblies. The medium goes through two stages to reach a higher pressure.

● Multistage Pump

In a multistage pump, the medium goes through various impellers or impeller chambers. In other words, the multistage pump builds up to the required pressure in stages.

Positive Displacement Pumps

While centrifugal pumps use centrifugal force to move a medium, positive displacement pumps use mechanical energy to accomplish the same thing. Moreover, unlike centrifugal pumps that require priming with the medium, positive displacement pumps are ordinarily self-priming.

Reciprocating Type Positive Displacement Pump

Reciprocating-type pumps use plungers, diaphragms, or pistons combined with valves to suck the medium in and move the medium out.

Reciprocating pumps may be single-acting or double-acting.

Single-acting pumps displace the medium with every forward stroke. Double acting pumps displace the medium in both the forward and return strokes.

● Piston Pump

When the piston goes up, the inlet valve opens, thereby letting the medium into the chamber. On the downstroke, the piston pushes on the medium, increasing the pressure in the chamber.

The inlet valve closes, while the high pressure causes the discharge valve to open and the medium to flow out.

● Plunger Pump

The plunger works pretty much like the piston in the piston pump. On the upstroke, the inlet valve opens, admitting the medium to the chamber. On the downstroke, the discharge valve opens to release the medium.

In this case, however, it is the mass of the plunger that displaces the medium. The number of plungers depends on pressure requirements. Triplex plunger designs, for instance, provide ultra high pressure for hydroblasting needs.

● Diaphragm Pump

The flexible diaphragm lets the medium in by increasing the volume of the chamber on its upward flex. On its downward flex, the diaphragm reduces the volume of the chamber, displacing the medium out of the chamber.

Rotary Type Positive Displacement Pump

The rotary type displacement pump is more common than the reciprocating positive displacement pump. In this type, gears, vanes, and lobes (among other types) move in a circular motion.

The circular motion moves the medium from one side (the suction side) to the other side (the discharge side).

Below are a few examples of rotary pumps.

● Gear Pump

There are two types of gear pumps: the internal gear pump and the external gear pump. Gear pumps utilize a set of gears. A motor drives one of the gears (i.e., the driven gear), while the driven gear’s motion moves the other gear (i.e., the idler).

As the medium enters the pump housing, it enters the gear teeth and remains trapped between the gear teeth and the pump casing.

The circular motion of the gears moves the trapped medium to the other side of the pump housing. At that point, the teeth of the two gears mesh, closing the gear teeth chamber and forcing the medium out of the pump housing and onto the discharge valve.

● Lobe Pumps

A rotary lobe pump uses two or more lobes (each independently driven by a rotor) that move in a circular, carefully timed motion.

As the medium enters the pump housing, the long outer side of a lobe and the housing wall forms a lobe chamber that traps the medium. The lobe then moves in a circular motion, transporting the medium to the other side and towards the outlet.

As the short side of the lobe meets the rotor of another lobe, the lobe chamber carrying the medium closes, displacing the medium, so it flows to the discharge valve.

● Vane Pumps

Vane pumps have a set of sliding vanes arranged on a rotor offset from the center.

These vanes slide in and out. They slide out as much as is required to meet the interior wall of the pump housing, creating a sealed chamber for transporting the medium.

When the medium enters the housing, two adjacent vanes trap it between them and the interior wall of the pump housing. As the vanes move, they carry the medium along with them to the other side.

At the outlet side, the offset rotor meets the interior wall of the housing. The vanes retract, the chamber closes, so the medium is displaced and flows out to the discharge valve.

Choose Your High Pressure Pump Type

As earlier mentioned, the above list is not nearly exhaustive. There are many other types of high pressure pumps.

To find the pump you need, consider your target application. Do you need ultra high pressure? Do you require high flow rates? Perhaps, you have variable pressure and flow rate requirements.

Next, consider your budget. The more precise, efficient, and versatile pumps typically cost more.

You should also consider maintenance requirements. Some pumps require more maintenance than others.

Whatever you do, do not choose a high pressure pump without carefully considering your needs, your particular use cases, and your options.

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