Principles of Positive Displacement Pumps

Principles of Positive Displacement Pumps | Flowmetrics

There are so many different pumps and meters these days. Picking the best one depends on what you need it to do. In some instances a positive displacement pump is necessary but, what is it they do exactly. With a positive displacement pump, liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is a constant given each cycle of operation. The positive displacement pumps can be divided in two main classes, reciprocating and rotary. 

Positive displacement pumps shouldn’t operate against closed valves on the discharge side of the pump. There is no shut off head on them like on centrifugal pumps. If so, operating against closed discharge valves continues to produce flow until the pressure in the discharge line is increased until the line bursts or the pump is severely damaged – or both.

For more about positive displacement pumps visit Engineering Toolbox HERE


Types of Fluid Flow Meters

Types of Fluid Flow Meters


Having options is always a great thing. There are many different types of flow meters on the market. The common principles of flow meters are differential pressure, velocity, positive displacement, mass, and open channel. Along with the principles the different types of meters are orifices, venturies, nozzles, rotameters, pitot tubes, calorimetrics, turbine, vortex, electromagnetic, doppler, ultrasonic, thermal and coriolis.

Because there are so many different types, making sure you have the right one for the project is imperative. Each meter does different things and reacts differently depending on what you need it for. The basic goal is to get the most accurate reading. 

For more information on what all these flow meters do visit Engineering Toolbox HERE


Video: What is a Positive Displacement Flow Meter


This video is an introduction to the positive displacement (volumetric) flow meter technology. It gives a basic overview of volumetric and positive displacement flow measurement and provides an example of flow calculation and output. Positive displacement flow meters measure the volumetric rate of moving fluid or gas by dividing the media into fixed, metered volumes (finite increments or volumes of the fluid).


For more on flow meters visit Max Machinery 

Meters Used In Custody Transfers

Meters Custody Transfers


One of the most important applications for flow measurement is custody transfer. There are many different meters used in custody transfers and in particularly positive displacement flow meters are highly regarded as a standard.

Using a positive displacement meter in custody transfers are highly accurate in the transfer of commercial and industrial water, as well as natural gas and other liquids. PD meters also are great for measuring low flows and high viscous flows. Another great reason for using a PD meter in custody transfers is that they capture the flow in a container known as volume, making speed of flow a non issue.

Other meters used in custody transfers are:

Differential Pressure Flow Meters

Turbine Flow Meters

Coriolis Flow Meters

Ultrasonic Flow Meters

Positive Displacement Flow Meters


For more info on these meters and their uses visit Flow Tech HERE







The Sundry Uses of Positive Displacement Flow

The Sundry Uses of Positive Displacement Flow | Flowmetrics

The Positive Displacement Flow Meter

The measurement of volumetric flow requires a relative degree of exactitude because a failure to this end could result in a breakdown in organizational decision-making. This is why a flow meter is essential for all those individuals and companies who have a vested interest in the functionality of flow rates. Of course, each situation requires unique engineering standards that adapt to the contextual constraints. The type of flow meter you choose will thus depend on a number of different factors, such as type of gas or liquid; minimum and maximum flow rates; whether the flow is continuous or not; and the maximum pressure at the location, just to name a few. It should also be stated that not every situation requires supreme accuracy. For instance, water flowing to a vineyard may only need accuracy of 5 to 10 percent, but for those applications that require a greater degree of precision, the positive displacement meter is probably the best bet, as it is the only device to directly measure exact volume. In the following, you will become acquainted with some of the applications of this nifty piece of equipment.


The Final Frontier of Flow


It might come as no surprise that one of the major users of this product is the National Aeronautics and Space Administration (NASA), along with many other aerospace and aviation companies. As you can imagine there is a great deal of liquid and gaseous flow to track, so the applications are many. The most notable use of this product is the detection and measurement of the flow of dinitrogen tetroxide, otherwise known as rocket propellant, using the 915 BATRT Field Indicator in explosion proof housing. How else could NASA engineers accurately measure the gargantuan amount of fuel flowing into those beastly ships?




It is easy to forget about all the labor that goes into the refinement of crude oils before they are injected into a nation of vehicles. A whole slew of additives have to be pumped into this natural resource, from simple surfactants to corrosion inhibitors. Chemicals, such as these, are injected at high pressures and have to be monitored to ensure accuracy. Because these chemicals vary in viscosity and density, the flow meter must be able to handle a number of different kinds of liquids. That is where positive displacement flow meters come in. Due to the tight spaces between moving parts, this type of flow meter is able to handle the high pressure rating. Without these specially made gadgets, the world economy might literally screech to a halt.


The List Is Too Long


There are too many possible uses to run through here. The list goes on and on. The following are some of the possible applications of positive displacement flow meters:


  • Hydraulic Test Stands
  • Batching and Mixing
  • Lubrication Oil Blending


Wherever there is need for an accurate measurement of volumetric flow, this ingenious trinket will be on call. For more information about the uses and advantages of this type of flow meter, look up a distributor online or in the phonebook. Talking to an expert can help you decide which flow meter is right for you.


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