Viscosity Rules for Oval Gear Meters

Viscosity Rules on Oval Gear Meters

Minimum Viscosity for Oval Gear Meters

For liquids below 3cP, the accuracy of your flowmeter is not guaranteed to be within the stated tolerance throughout the standard flow rangeIt may be necessary to increase the minimum flow rate specification to above 10% of maximum flow in order to obtain the required measurement accuracy. For liquids between 1-3cP the influence on measurement accuracy will be very small provided that the

liquid being measured has reasonable lubricating qualities,and should be of no concern in most systems.

OM025 reads between 2.6 and 40 GPM

Below 3 cP the minimum becomes 10% of the Maximum (4 - 40 GPM)

Very Dry (non-lubricating) Thin Liquids

The most difficult liquids to measure with a PD flowmeter are non-lubricating liquids with viscosities below cP; measurement accuracy most often suffers below 10% of maximum flow rate (see above), and flowmeter life-span will suffer with extended periods of use above 80% of maximum. If you have purchased an Oval Gear meter to measure this type of liquid, it is advisable to restrict the flow rate to

greater than 10% of the maximum flow rating for your meter, and less than 80% of maximum flow rating for any continuous use.

OM025 reads between 2.6 and 40 GPM

Below 3cP the minimum becomes 10% of the Maximum and very thin non-lubricating liquids the Maximum drops to 80% of the Maximum (4 - 32 GPM)

Viscosities above 1000cP

When viscosities are above 1000 cP, the maximum flow rate has to be de-rated to keep the maximum pressure drop across the meter below 14.5 psi (1Bar)High Viscosity rotors will reduce the pressure drop across the meter by approximately 50% (See Flow Rate De-Rating Guide on next page).

If you find that your liquid viscosity is greater than l000cP and your meter is fitted with standard rotors (or 2000cP for high viscosity rotors), you will need to check that your maximum flow rate is reduced in accordance with the viscosity de-rating chart (next page)Running your flowmeter above the maximum de-rated flow on a high viscosity liquid will cause shaft and/or bearing damage that is not covered under warranty If your flow rate requirements can not be achieved for your high viscosity liquid, you can either retrofit the meter with High Viscosity rotors, or purchase a larger size of Oval Gear meter.
  Maximum Flow Multiplier for PD Meters
less than
Standard Oval Gear With High Viscosity Rotors
1,000 cp 1.00 1.00
2,000 cp 0.50 1.00
4,000 cp 0.42 0.84
6,000 cp 0.33 0.66
8,000 cp 0.25 0.50
30,000 cp 0.15 0.30
60,000 cp 0.12 0.25
150,000 cp 0.10 0.20
250,000 cp 0.05 0.10
1,000,000 cp 0.025 0.05

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