volumetric meter

7/27/2019 Volumetric Meter

1/8

Volumetric Meter (Positive Displacement Flow meter)

Positive displacement flow meters, also known as PD meters, measure volumes of fluid

flowing through by counting repeatedly the filling and discharging of known fixed volumes. Atypical positive displacement flow meter comprises a chamber that obstructs the flow. Inside

the chamber, a rotating/reciprocating mechanical unit is placed to create fixed-volume discrete

parcels from the passing fluid. Hence, the volume of the fluid that passes the chamber can be

obtained by counting the number of passing parcels or equivalently the number rounds of the

rotating/reciprocating mechanical device. The volume flow rate can be calculated from the

revolution rate of the mechanical device. The behavior and the minimum amount or maximum

amounts of flow that can be reliably read by a specific positive flow meter will depend on the

geometry used in the mechanical rotating and moving parts.

Many types of positive displacement flow meters are used in the industry. They are

named after the mechanical device inside the chamber. They all share the same principle of

operation and are volumetric flow measuring instruments.


2/8

Oscillating Piston

1.1DefinitionLiquid enters a precision-machined chamber containing an oscillating (rotating) piston.

The position of the piston divides the chamber into compartments containing an exact volume.

Liquid pressure drives the piston to oscillate and rotate on its center hub. The movements of

the hub are sensed through the meter wall by a follower magnet. Each revolution of the piston

hub is equivalent to a fixed volume of fluid, which is indicated as flow by an indicator/totalizer.

Close clearances between the piston and the chamber ensure minimum liquid slip for highly

accurate and repeatable measurement of each volume cycle. Maximum viscosity allowed: 4,000

centipoise.

1.2. Operating parameters

Accuracy 0.2% - 0.5% in full rate

Turndown 10:1

Pipe sizes 10 to 50mm

Maximum pressure 2.94MPa

Temperature range 10 to +120C


3/8

1.3ApplicationsPositive Displacement Flow Meters high precision has allowed it to be almost

universally accepted for billing and transfer standard applications, such as gasoline and fuel

oil dispensing, natural gas or water measurement.

Oval Gear Flow meter

2.1DefinitionThe design of the oval gear flowmeter is relatively simple; oval shaped gear-toothed

rotors rotate within a chamber of specified geometry. As these rotors turn, they sweep out and

trap a very precise volume of fluid between the outer oval shape of the gears and the inner

chamber walls with none of the fluid actually passing through the gear teeth.


4/8

Normally, magnets are embedded in the rotors which then can actuate a reed switch or

provide a pulse output via a Hall Effect sensor. Each pulse or switch closure then represents a

precise increment of liquid volume that passes through the meter. The result is a high degree of

accuracy (.5 percent of reading) and resolution and almost negligible effects for varying fluid

viscosity, density and temperature.


Accuracy 0.5% - 2% in full rate

Turndown 10:1

Pipe sizes 10 to 250mm

Maximum pressure 6.4MPa

Temperature range -20 to 200C

2.3ApplicationsGear flow meter provides precise volumetric flow measurement of clean liquids found in

a broad range of industries including automotive, aviation, mining, power, chemical,

pharmaceutical, food, paint & petroleum. Applications include the distribution of fuels, fuel

oils, lubricants, alcohols, solvents, blending of bio & ethanol fuels, metering of chemicals,

grease, adhesives, ink, insecticides & non-conductive liquids either pumped or gravity fed.

Nutating Disc

3.1DefinitionThe movable element is a circular disk which is attached to a central ball. A shaft is

fastened to the ball and held in an inclined position by a cam or roller. The disk is mounted in a

chamber which has spherical side walls and conical top and bottom surfaces. The fluid enters

an opening in the spherical wall on one side of the partition and leaves through the other side.

As the fluid flows through the chamber, the disk wobbles, or executes a nutating motion. Since

the volume of fluid required to make the disc complete one revolution is known, the total flow

through a nutating disc can be calculated by multiplying the number of disc rotations by the

known volume of fluid.


5/8


Accuracy 0.5% - 1.5% in full rate

Turndown 10:1

Pipe sizes 1 inch

Maximum pressure 125psi

Temperature range -10 to 130F

3.3ApplicationsNutating Disc positive displacement flowmeters measure any liquid including viscous

fluids such as asphalt, corn syrup, glue and corrosive liquids.


6/8

Roots (Rotary)

4.1DefinitionRotary meters are highly machined precision instruments capable of handling higher

volumes and pressures than diaphragm meters. Within the meter, two figure "8" shaped lobes,

the rotors (also known as impellers or pistons), spin in precise alignment. With each turn, they

move a specific quantity of gas through the meter. The operating principle is similar to that of a

Roots blower. The rotational movement of the crank shaft serves as a primary flow element

and may produce electrical pulses for a flow computer or may drive an odometer-like counter.


Accuracy 0.2% - 0.5 % in full rate

Turndown 20:1

Pipe sizes 50 200mm

Maximum pressure 6.3Mpa



7/8


8/8


Accuracy 0.5% - 1 % in full rate

Turndown 15:1

Pipe sizes 20 300mm

Maximum pressure 4Mpa


5.3ApplicationsDiaphragm gas meters most often are used to measure the flow of natural gas,

especially in metering consumption by households.

For all positive displacement flow meters:

Pros:

- Low to medium initial set up cost

- Can be used in viscous liquid flow

Cons:

- Higher maintenance cost than other non-obstructive flowmeters

- High pressure drop due to its total obstruction on the flow path

- Not suitable for low flow rate

- Very low tolerance to suspension in flow (particles larger than 100 m need tobe filtered before the liquid enters the flowmeter)

- Gas (bubbles) in liquid could significantly decrease the accuracy

volumetric meter

Documents