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Common Types of Hydraulic Flow Meters Cheat Sheet (DRAFT) by [deleted]

Common types of hydraulic flow meter

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Introd­uction: What is flow?

Flow is the measur­ement of the volume of a liquid that passes a fixed point in a unit of time. For most hydraulic applic­ations, flow is measured in liters per minute (lpm), U.S. gallons per minute (US gpm), or, occasi­onally, U.K. gallons per minutes (UK gpm).

Multiply By To obtain
US gpm 3.785 lpm
UK gpm 4.546 lpm

Flow Meter

What to consider when selecting a flow meter?

When searching for a flow meter for use in a particular hydraulic applic­ation, these five questions can help:
1. What are the fluid proper­ties?
2. What are the hydraulic system operating condit­ions?
3. Why is flow being measured; how accurate does the flow measur­ement need to be?
4. What effect might the flow meter have on the fluid and vice-v­ersa?
5. How important is it to measure flow; what is your budget?

Variable orifice flow meters

The idea of flow displacing an object, usually a piston or a ring, forms the basis of simple ‘variable orifice’ flow meters. The momentum of the fluid exerts a force on a piston that is held in place by a spring. Such meters typically have an accuracy of between 2 – 5% of full scale

Gear type flow meters

These are positive displa­cement flow meters. On the inside, they look similar to a gear-type motor. Fluid passes around the outside of a pair of interm­eshed gears, rotating the gears on their shafts. A transducer mounted above one of the gears generates a pulse each time a gear tooth passes under it. The rotation of the gears is propor­tional to the flow rate. Sometimes, two transd­ucers are used to measure direction and improve resolution

Turbin­e-type flow meters

In a turbin­e-type flow meter, a turbine rotor is mounted on a shaft between two sets of flow straig­hte­ners. The fluid passes through the flow meter and rotates the turbine blade. As for a gear-type flow meter, a transducer is mounted above the turbine and generates a pulse each time a blade passes under it. The frequency from the transducer is propor­tional to the flow over a limited range.

Other Meter Types

Oval gear meters are similar to conven­tional gear meters, but use two elliptical gears that rotate together at 90º to one another inside a housing. The fluid is swept around the chamber by the gears, and the frequency of rotation is directly related to the volume of fluid through the meter.