Positive Displacement Flow meters

How Positive Displacement Flow meters Work

Excellent stepless adjusting mechine;
High accuracy and repeatability over the widest range of flow; Superior accuracy at constant flow;
Low maintenance, no metal-to-metal contact in measuring chamber, Long life service;
Low pressure loss, a true gravity flow meter;
Accuracy regardless of pressure fluctuations, temperature variation, viscosity;
Choice of aluminum, cast iron, brass and stainless steel materials of construction.

Industries
Automotive; Adhesives; Agriculture; Asphalt ; Aviation fueling ; Animal feeds; Beverage; Cosmetics ; Chemical processing; Concrete Add mixtures; Dairy; Liquid fertilizers; Food processing ; Fuel oil delivery; General industrial; Hydrocarbon processing; Liquefied gases; Lube oils; Marine ; Paint and varnish ; Petroleum marketing ; Petroleum production ; Pharmaceutical; Printing ink; Pulp &paper; Refining commercial Solvents; Recycling Railroad ; Textile.
Positive displacement flowmeters repeatedly entrap fluid to measure its flow. It can be thought of as repeatedly filling a bucket with fluid before dumping the contents downstream. The number of times that the bucket is filled represents the flow. Many positive displacement flowmeter geometries are available.  
 
How to Use Positive Displacement Flowm eters
Positive displacement flowmeters measure the volumetric flow of fluids in pipes, such as water, hydrocarbons, cryogenic liquids, and chemicals. Some designs can measure gas flow. In liquid service, increasing viscosity decreases slippage and increases the pressure drop across the flowmeter. A large pressure drop across the flowmeter can prematurely wear and/or damage bearings and/or seals. Note that flowmeter size may increase to reduce the pressure drop in these applications. 
Be careful because damaging the sealing surfaces by will increase slippage and degrade measurement accuracy. Using positive displacement flowmeters in abrasive or dirty fluids can cause maintenance problems because of potential damage to the sealing surfaces, damage to the bearings, and/or plugging of the flowmeter. A filter may be required to remove dirt. 
Be sure that gas bubbles are removed from liquid flow streams when using positive displacement flowmeters. Flow measurement taken with bubbles will be higher than the true liquid flow because the bubble volumes will be measured as if they were a volume of liquid. A gas eliminator may be required to remove bubbles. 
This flowmeter can be applied to clean, sanitary, and corrosive liquids, such as water and foods, and some gases. Materials of construction are important because small amounts of corrosion or abrasion can damage the sealing surfaces and adversely affect measurement accuracy. In addition, consideration should be given to all wetted parts, including the body, rotating parts, bearings and gaskets. 
Many positive displacement flowmeters are used in municipal water districts to measure residential water consumption. 
Corrosive liquid applications are commonly found in the chemical industry processes, and in chemical feed systems used in most industries. 

Application Cautions for Positive Displacement Flow meters