Do you know the advantages of positive displacement pumps, but are still undecided as to which types of positive displacement pumps are best suited to your needs?

In this article you will find an overview and an initial decision-making aid.

Show all series.

First of all: How do positive displacement pumps work?

Before we go into the different types of positive displacement pumps, here is a brief explanation of how they work:

Positive displacement pumps work, as the name suggests, according to the positive displacement principle. Put simply, a positive displacement pump collects liquid and forces it into the pressure line. This movement is triggered (in the case of screw pumps, for example) by two or three spindles that move in opposite directions and thus displace the liquid.

Closed displacement volumes ("chambers") are formed and the liquid is conveyed under constant pressure. Due to this operating principle, the liquid cannot flow in the opposite direction even when the pump is stationary.

KRAL - Your expert for pump technology.

"Quality, innovation and speed, at all times and worldwide."

Since the company was founded, KRAL has positioned itself as a manufacturer of quality products at a fair price/performance ratio, offering customized solutions for systems, from engineering to commissioning, both locally and worldwide. Our after-sales service is also there for you after your purchase.

Convince yourself of our services. We are here for you.

Make a request

Types of positive displacement pumps and their advantages.

In the case of positive displacement pumps, a basic distinction is made between the oscillating positive displacement pump (piston pump, diaphragm pump) and the rotating variant (gear pump, impeller pump, impeller pump, peristaltic pump, etc.).

The great advantage of all positive displacement pumps - whether rotating or oscillating - is that, unlike other types of pumps (e.g. flow pumps), they allow an almost constant flow rate, regardless of pressure changes, viscosities and temperature fluctuations.

The efficiency of a positive displacement pump can be many times higher than that of other pump types in cases where high differential pressures, high viscosities and strong temperature fluctuations can occur.

The question is therefore often not whether a positive displacement pump is yes or no, but rather which type of positive displacement pump is the best for the particular application given the large selection available.

Gear pumps, for example, have the disadvantage that the bearing is located in the pumped liquid, which makes them sensitive to solids and also deflects the liquid.

Rotary lobe pumps, on the other hand, allow solids but have poor suction characteristics and are also not suitable for high speeds.

Impeller pumps have good suction characteristics, but are less suitable for high viscosities and high differential pressures.

Peristaltic pumps: These are also not suitable for high differential pressures. Only low speeds are possible and the medium is also squeezed. Their service life is also short.

Althoughimpeller pumps are simple in design, they are only suitable for low pressures and their power density is low.

In view of the advantages and disadvantages listed above, the screw pump has proven to be the optimum choice in many cases, which is why KRAL, for example, has specialized in it.

X

Flexible connections

If the outer casing of the screw pump is made of steel, almost any position, direction, size, type and classification of the flange is possible. It can be optimally adapted to any installation situation.

X

Housing variants

Depending on the operating requirements, the CG series screw pumps are available with cast iron or steel housings.

X

External overflow valve

The overflow valve ensures that the liquid is diverted in the event of overpressure.

X

Rotary shaft seal

The CK series screw pump is only available with a radial shaft seal. The CL series screw pump can be equipped with different shaft seals thanks to the longer spindle set. External ball bearings are also possible. This pump line is used as a horizontal or vertical foot pump or flange pump as well as a vertical container pump.

X

Seal housing

Depending on the operating requirements, different shaft seals are possible for the CL series. The CL screw pump is the slide-in pump used in the CG series. The different housing options allow enormous flexibility in terms of fluid connections. An optional external overflow valve can be fitted to CG screw pumps.

X

Longer spindle set

Thanks to the longer spindle set, external ball bearings are also available as an option.

Types of positive displacement pumps and their advantages.

The advantages of the screw pump are obvious. They are quiet, they pump gently (no squeezing of the medium!), have very good suction characteristics, high efficiency and a long service life. They are also generally low-maintenance.

Both the 2-spindle screw pump and the 3-spindle screw pump should be mentioned here.

The advantages of the 3-spindle screw pump in particular are:

They pump liquids particularly gently and quietly.
High power density.
Constant flow rate.
No pressure pulses that could damage components or cause vibrations.
Pressure-stiff characteristic curve (the flow rate is hardly reduced when the pressure is increased).

Do you have any questions? - We will be happy to help you!

We and our independent sales and service partners are available to you worldwide at any time.
Please contact us by phone or e-mail or use our inquiry form and we will get back to you shortly.

Our contact persons

Make a request

Conclusion.

As the viscosity of the liquids to be pumped increases, positive displacement pumps are indispensable. They are also necessary when working with different pressures or with large temperature fluctuations. In many applications, the screw pump is a reliable choice in terms of price-performance ratio.

Nevertheless, the pumped liquid, operating conditions, installation location, standards and guidelines must also be taken into account when deciding on a screw pump. It is worth obtaining competent and individual advice here. The experienced pump experts at KRAL will be happy to advise you on your individual requirements.

Positive displacement pumps by application.

Oil and gas industry: transporting crude oil, refinery products and chemical processes.
Chemical industry: transportation of chemicals, acids, alkalis and other aggressive liquids.
Marine and shipping: Bilge dewatering, fuel supply, ballast water handling.
Power generation: Feeding fuel into gas turbines, pumping coolants.
Mining and mineral processing: pumping slurries, abrasive media and dense liquids.
Agriculture: Irrigation, fertilizer metering, and animal feed production.