Positive Displacement Flowmeter – A Complete Guide

Introduction

A positive displacement flowmeter is a technology that measures the flow of fluid that passes from the flowmeter. It achieves this by trapping fluid between rotators with high precision and accuracy.

In this paper, we will discuss the positive displacement flowmeter in detail. You can get the answers to your questions if you have been looking forward to using a positive displacement flowmeter for your company. The FAQs will briefly discuss the common questions.

1. What is a Positive displacement flowmeter?

A positive displacement flowmeter is the only flow measuring technology that directly measures the volume of fluid that passes through the flowmeter. It can be done by trapping pockets of fluid. In these flowmeters, the rotating components contain magnets that activate sensors outside the chamber. As a result, a positive displacement flowmeter provides excellent accuracy and repeatability in a wide range of applications.

Positive displacement flowmeters are considered the workhorses of today’s flowmeters. It measures the volumetric flow rate of fluid gas by dividing it into fixed and metered volumes. It can measure the low flow of fluids because its components are not balanced hydraulically. Instead, they are mass balanced.

2. What are the applications of Positive displacement flowmeter?

Many applications use Positive displacement flowmeters. Some of them are below.

• Measurement of the direct flow of fluids or gasses in pipes.
• Chemical industries to accurately calculate the flow of viscous fluids and other chemicals.
• Positive displacement flowmeter uses volumetric flow measurement of petrochemicals, paints, and dyes.
• Measurement of various chemicals for making batches in pharmaceutical laboratories.
• In hydraulic testing, chemical dosing, pharmaceutical applications, and other related applications.
• You can use it for the measurement of highly viscous and dirty fluid. But, you can also use clean and non-erosive fluid for accurate measurement in various applications such as inventory management of chemicals ranging from detergents to low concentrated acid solutions.
• To monitor fuel consumption for generators in construction sites.
• Although they are ideal for measuring viscous liquids, a Positive displacement flowmeter measures less viscous fluids like water, organic solvents, or alcohol.
• Also suitable for measuring food processing with edible oils, honey, and molasses.

3. What are the types of Positive displacement flowmeters?

• Reciprocating or Oscillating Piston

This Positive displacement flowmeter uses a mechanically or magnetically operated piston for filling the cylinder with fluid.

• Gear

Gear flowmeter depends on internal gears that rotate as the fluid passes through them. There are various types of gear based on their shape. For example, oval gear has two rotating oval gears that squeeze fluid through the meter. As the flow rate increases, so does the rotation of rotors. Helical gear has a spiral-shaped structure. Fluid enters the compartments in rotors which causes rotation.

• Nutating Disk

A nutating disc flow meter has a round disc on a cylindrical chamber. The flow meter measures the number of times the chamber fills and empties fluid and consider as the widely used Positive displacement flowmeter. They are best for pressure ranges around 150-PSIG with an upper limit of 300 PSIG. The liquid enters the chamber using the disc, which divides the chamber into compartments.

• Roots flowmeters

Roots flowmeters are somewhat similar to the oval gear flowmeter. It consists of two-lobed impellers which rotate in opposite directions. You can measure fluid measurement by measuring the rotation speed; the maximum range of viscosity for this PD flowmeter is 5000 centipoise.

4. What are the advantages of a Positive displacement flowmeter?

• Positive displacement flowmeters are very accurate, reliable, and have high turndown.
• They measure viscous and corrosive fluids and require no straight runs of pipe.
• Positive displacement flowmeter uses custody transfer of oil and fluids, in-home natural gas, and metering.
• Positive displacement flowmeters with internal wiping seals have the highest differential pressure.
• They are suitable for fluids with high viscosity.
• They require little or no maintenance and have a long life.

5. What are the Disadvantages of a Positive displacement flowmeter?

• Some models of the Positive displacement flowmeter have low-quality material; therefore, corrosion can be a concern.
• Positive displacement flowmeters can block the flow if any larger particle is trapped.
• PD flowmeters are relatively larger and heavier than the differential pressure flowmeters.
• They can measure high viscosity fluid with accuracy. However, this flowmeter is less accurate with low viscosity fluid or gas because of excessive leakage in the internal sealing surface.
• The internal moving parts are subject to wear.
• A positive displacement flowmeter is not suitable for sticky and abrasive fluids.
• The change in fluid flow can damage the moving parts because of inertia.

6. How Positive displacement flowmeter works?

Positive displacement flowmeter performs necessary flow measurements such as billing for water and gas in residential and commercial applications. In addition, PD flowmeters are the best solution for specific applications in high viscosity liquids and low flow measurements.

A positive displacement flowmeter separates the fluid into various components. It measures the flow rate by the number of times gas or liquid is filled and refilled. It consists of chambers that hinder the media flow and a rotating mechanism that allows the passage for fixed volume amounts.

7. How to calibrate a Positive displacement flowmeter?

A positive displacement flowmeter is a device made to measure the fluid flow through the space within a more extensive system. Various businesses use PD flowmeters, including agriculture, aerospace, petrochemical, and chemical. To ensure the working of the flowmeter effectively, you should do calibration so that the readings are accurate.

The calibration is done by following the specific calculations and measurement standards set by the industry. The calibration makes sure that each meter is working properly and giving reliable outputs. For example, in the calibration of the Positive displacement flowmeter, series of minor adjustments are made based on comparing the readings of the meter being calibrated and the accurate flow rate measured by the meter.

8. Why calibrate Positive displacement flowmeter?

It is essential to understand that all flowmeters require calibration regularly to avoid any inaccuracy. The flowmeters get degraded over time that affects their performance. For instance, debris or corrosion can impact outputs. A positive displacement flowmeter depends on fluid measurement and surrounding conditions. The only way to ensure accuracy is to perform maintenance.

It is best to use the tracing standard when calibrating the Positive displacement flowmeter, which means complying with national standards. If a meter suspends of having an inaccurate range, it is best to send it for calibration. Before calibrating the flowmeter, it is rational to aim for a result that has a higher standard than the one you want to achieve.

9. How is the calibration of the Positive displacement flowmeter work?

Positive displacement flowmeter, as mentioned above, depending on moving parts to measure fluid, and these parts must be locked with one another to avoid any leakage. These parts are built with the components of high precision, rotating components, and inlet and outlet. For maintaining the performance of your flowmeter, it is best to use a traceable standard.

Upon installation, the final calibration in the positive displacement flowmeter is done to compensate for the differences between actual metered liquids and test liquids. For example, if the weighing machine indicates a weight of 2kg without putting anything, it needs calibration. To perform calibration, place the meter under test and then compare the master flow meter and flow meter readings using the measured volume of liquid.

10. What is the accuracy range of the positive displacement flowmeter?

A positive displacement flowmeter is highly useful for measuring liquids of high viscosities, making them very accurate. They are ideal for remote sites that require low maintenance as they permit operation with both voltage pulse signals and mechanical registers.

Overall Positive displacement flowmeters are very accurate with high turndown. PD meters can measure both liquid and gases accurately. They work best with clean, non-erosive, and non-corrosive liquid and gases. They provide better relative accuracy at low flows than office-type flowmeters.

How to install a Positive displacement flowmeter?

Positive displacement flowmeter does not require a power supply for their operation, neither do they need upstream and downstream run for their installation. PD flowmeters can operate with turndowns as high as 100:1, although ranges or 15:1 or below are more common, and filtering is made for particles greater than 100microns in size.

Positive displacement flow meters operate with small clearances between the precision parts, and wear destroys their accuracy. However, you can install them in vertical or horizontal orientation.

11. On what kind of fluids Positive displacement flowmeter is applicable?

A positive displacement flowmeter measures clean, sanitary, corrosive liquids, such as water, food, and gases. However, some models of PD flowmeter can tolerate some impurities. They can work best in both liquids and gases. Some models of this flowmeter only allow the measurement of lubricating fluid because fluid exposes the rotor.

They are different from turbine meters because they handle high viscosity liquids. This is the reason they can measure the hydraulic fluids as well. Positive displacement flowmeters are used primarily for smaller pipe sizes. For example, PD meters for gas applications measure 1 ½ inch and 10 inches.

12. How reliable is a Positive displacement flowmeter?

A positive displacement flowmeter performs well for an extended period if the fluids are clean, non-corrosive, and properly maintained. In small measuring systems, such as domestic water and gas, meters need testing every year.  In large industries such as the petroleum industry, Positive displacement flowmeters need testing every week.

PD meters are highly reliable, provide high precision of internal components, and have good repeatability. Their accuracy is not affected by pulsating flow. Designs of Positive displacement flowmeter do not require upstream and downstream in the installation.

13. Limitations and considerations while choosing a Positive displacement flowmeter?

A positive displacement flowmeter offers many benefits for industries. However, there are certain limitations to their usage. Firstly, you can’t use them for fluids with large particles. This is because you filter the particles before they enter the measuring chamber. PD flowmeter cannot measure fluid having more amount of air.

Positive displacement flowmeters are relatively heavier and more costly than other non-positive displacement types such as magnetic or vortex flow meters. Another factor that you need to consider is that PD flowmeters cause pressure drops.

How to Maintain a Positive displacement flowmeter?

While using a Positive displacement flowmeter, some issues may arise, like pressure drops. These are mostly insignificant, but they are alarming in case of more significant pressure drops. Larger pressure drops can damage internal bearings and seals.

To overcome this problem, manufacturers usually use operating pressure values to prevent premature wear and flowmeter failure. One crucial technique to maintain the Positive displacement flowmeter is through calibration. A well-calibrated flowmeter provides accurate readings and keeps the system run smoothly.

14. Which industries use Positive displacement flowmeters?

A positive displacement flowmeter responds directly to fluid flow and can measure the flow with maximum accuracy. These are bulk meters suitable for many industries such as aviation, tank calibration, ship bunkering, etc. In addition, you can use a positive displacement flowmeter in custody transfer and residential home natural gas.

Many chemical industries use DP flowmeters to estimate viscous liquid flow and other hydrocarbon and cryogenic liquids. DP flowmeters are an effective tool to measure fluids in the food, beverage, and tobacco industry.

15. What are the cautions while using a Positive displacement flowmeter?

While using a Positive displacement flowmeter, avoid measuring dirty fluids in the flowmeter. First, you need to remove the dirt upstream of the flow meter. If you do not take these precautions, dirty fluid can cause plugging hence increasing the maintenance cost. Second, be more careful while selecting the bearing because the non-lubricating nature of some liquids can increase bearing.

When you measure the liquid, make sure there are no gas bubbles. First, effectively removes the bubbles because as viscosity increases, the pressure drop becomes acceptable. Second, it would help if you balanced the viscosity of operating fluid with calibrated fluid.

16. Which Positive displacement flowmeter is popular?

You can classify quantity meters as Positive displacement flowmeters. The other standard Positive displacement flowmeters are reciprocating piston, rotating piston, sliding and rotating vanes, nutating disc, gear and lobbed impeller, and other meters commonly used for measuring small quantities of gas at low flow.

All the DP flowmeters are very precise instruments and use accurate measuring of the fluids. Moreover, they provide operation at very low flows without the loss of accuracy. Thus, they are not only robust but also require little maintenance.

17. What is the working principle of a Positive displacement flowmeter?

Positive displacement flowmeters measure the volume of fluid in precisely known volumes. Their internal moving components are mass balanced yet hydraulically imbalanced. This results in the measurement of both liquids and gases without using external power.

Each moving chamber of fluid is separated from the other chamber by a capillary seal. Thus, there is a high precision of flowmeters. The internal metering of flowmeters requires a positive displacement flowmeter for clean liquids. These flowmeters are generally used in unidirectional flow measurements such as oil dispensing, natural gas, or water flowmeters. Advanced technology has made flowmeters’ temperature compensated with central control systems.

18. What is the effect of temperature on a Positive displacement flowmeter?

In various applications, a Positive displacement flowmeter measures mass flow in addition to volumetric flow. When the temperature of the liquid rises, it causes both the liquid and flowmeter body to expand.  Liquid expands more than the flowmeter. Some Positive displacement flowmeters allow some fluid to leak through the flowmeter. This is called slippage, and it makes the PD flowmeter under the register.

In fluid measurement, the density of gas and liquid changes when the temperature is changed. When the temperature of the fluid increases, its viscosity decreases. This increases slippage and allows more liquid to pass through the measuring chamber.

19. How is the Positive displacement flowmeter operated?

Positive displacement flowmeter operates based on three components; inlet and outlet ports, measuring chamber, and one or more rotors. Fluid enters the chamber through the inlet port and transmits energy on the rotor. The rotation of the rotor corresponds to the amount of fluid entering the chamber. The fluid then exits the chamber through the outlet port.

The rotors have two gears, and gears can be circular or oval-shaped and attached horizontally or vertically. The purpose of the two gears is to create the seal in the measuring chamber. This seal measures the fluid before entering the chamber. Other Positive displacement flowmeters have helical or screw-shaped gears.

20. What are the components of a Positive displacement flowmeter?

A positive displacement flowmeter is the volumetric flow instrument that measures the precise volume of fluid with each revolution. Their internal moving components are hydraulically locked with the amount of liquid moving through the flowmeter. As a result, PD meters can measure very low flow rates and flow rates of liquid with high viscosity.

Positive displacement flowmeter moves when the fluid moves and stops when the fluid stops. The two primary components of the PD flowmeter are sensor-only systems and transducers. They provide electronic outputs for controllers or data acquisition systems. In both types of Positive displacement flowmeter, performance specifications include operating pressure, temperature range, maximum material viscosity, connection size, and accuracy.

21. What are the performance characteristics of a Positive displacement flowmeter?

 A positive displacement flowmeter depends on the moving parts to measure fluid, and these moving parts must seal against one another to prevent leakage. Therefore, the main characteristic of any PD flowmeter is that the mechanism cannot move without fluid passage. As a result, the Positive displacement flowmeters are simpler in design and construction.

The PD principle is the only accurate method of measuring fluid flow. The mechanical components of the DP flowmeter suffer damage from grit or other corrosive material present in the fluid. It is an instrument built to measure the individual volumes of fluid. These instruments are completely immune, and you can install them near the piping system. Positive displacement flowmeters are very linear as the machine cycle is directly proportional to fluid volume.

22. How Positive displacement flowmeter hold a place in Utility Measurement?

A positive displacement flowmeter is an important flowmeter in today’s flow meter world. They are considered as workhorses of the world’s flowmeter. This is because they make essential flow measurements that many people take for granted. The PD flowmeter also measures how much water you have used at your house most of the time.

There are different shapes and sizes of their compartments depending on the design for liquids or gases. Therefore, a positive displacement flowmeter makes cost-effective mechanical measurements for utility purposes. For utility purposes, the main competition of PD meters is a single jet, multi-jet, and Woltman turbine meters.

23. Is a Positive displacement flowmeter a popular choice in industries?

Positive displacement flowmeter is the traditional technology flowmeter with popularity all around the world. Although PD flowmeter faces stiff competition with other new technology flowmeters, it is still the best solution for specific applications. For example, a positive displacement flowmeter is an effective flowmeter for low-cost mechanical measurements.

Positive displacement flowmeter is very popular in commercial and residential gas metering. However, PD meters rise and fall in demand because of their place in retail applications.

Conclusion

Overall, a Positive displacement flowmeter is an effective flowmeter for measuring the volumetric flow of fluids. They can handle high viscous fluid, and they do not require filtration before processing. If you want to purchase the flowmeter, our company will assist you in providing related information about the Positive displacement flowmeter.

Instruthinkis the most popular and renowned company with high customer ratings. We are the manufacturers of Positive displacement flowmeters and ensure the sustainability of our flowmeters. You can contact us at sales@instruthink.com in case of any queries.