PD flowmeters

Positive displacement (PD) flowmeters are truly a member of the class of traditional technology flowmeters. Their history goes back to 1815, when Samuel Clegg invented the first PD gas flowmeter. This was a water sealed rotating drum meter. Cleggs son-in-law, John Malam, together with Samuel Crosley, invented an improved model in 1825. Problems rem... ained, however, with high cost, freezing, and large size. Thomas Glover invented the first dry gas diaphragm meter in 1843. Glovers meter contained two diaphragms and a sliding valve. In 1844, the first actual dry gas meter was developed by engineers Croll & Richards. The diaphragm meters used today are similar to these early meters, although major improvements have been made in material of construction. Early meters had diaphragms made of sheepskin with steel metal enclosures. More recent meters have synthetic rubber-on-cloth diaphragms and are made of cast aluminum. , which introduced the oval gear meter in the early 1950s. Oval gear meters are used for liquid measurement. They are quite popular for oil applications, especially for downstream oil distribution involving custody transfer. Here they compete with Coriolis meters, which are gaining market share in downstream oil measurement. PD flowmeters operate by repeatedly filling and emptying compartments of known volume with the liquid or gas from the flowstream. Flowrate is calculated based on the number of times these compartments are filled and emptied. The main types of PD flowmeters used for gas applications are diaphragm and rotary. These types of meters differ according to the way they trap the liquid into compartments with different shapes. Diaphragm meters have several diaphragms that capture the fluid as it passes through the meter. Differential pressure across the meter causes one diaphragm to expand and one to contract. A rotating crank mechanism helps produce a smooth flow of gas through the meter. This mechanism is connected via gearing to the index, which registers the amount of fluid that passes ...Read More