Top Page > Product Information > Principle of Variable Flow Meter(Rotameter) > Principle of Flow meter (Float Type) 3.
Principle of Variable Flow Meter(Rotameter)
- Principle of Flow meter (Float Type) 3.
- The upper section of a fl ow meter is on the outlet side, while the lower section is on the inlet side.
1.
The equivalent flow chart of the upper and lower valves is shown in the figure.
The pressure loss of a flow meter is very small, not caus-ing any problem when a flow meter is used individually.
In the case of a flow meter with a valve, however, the inlet side pressure and outlet side pressure are important.
The valve installed in a flow meter causes a pressure loss, generating a difference between the inlet pressure and outlet pressure. As shown on page 50, the reading of a fl oat type flow meter differs according to the applied pressure.
There-fore, for flow meters with a valve, care is needed to see what will be the applied pressure.
In such cases, the inlet pressure P1 is throttled by a needle valve, changing into P2 at the outlet.
In the lower section, this P2 is the pressure applied to the flow meter. When there is no signifi cant load resistance (similar to atmospheric conditions) at the outlet and the subsequent section, P2 can be regarded as 0 MPa · G (gauge pressure), and as no pressure is applied to the flow meter, a general flow meter is used for calibration. (Refer to the atmospheric scale on page 50.)
Since operating pressure conditions are necessary for valves, however, it is necessary to clearly indicate P1 and P2when placing an order. Please indicate P2 as well when there is load resis-tance (when P2 pressure exist).
The pressure loss of a flow meter is very small, not caus-ing any problem when a flow meter is used individually.
In the case of a flow meter with a valve, however, the inlet side pressure and outlet side pressure are important.
The valve installed in a flow meter causes a pressure loss, generating a difference between the inlet pressure and outlet pressure. As shown on page 50, the reading of a fl oat type flow meter differs according to the applied pressure.
There-fore, for flow meters with a valve, care is needed to see what will be the applied pressure.
In such cases, the inlet pressure P1 is throttled by a needle valve, changing into P2 at the outlet.
In the lower section, this P2 is the pressure applied to the flow meter. When there is no signifi cant load resistance (similar to atmospheric conditions) at the outlet and the subsequent section, P2 can be regarded as 0 MPa · G (gauge pressure), and as no pressure is applied to the flow meter, a general flow meter is used for calibration. (Refer to the atmospheric scale on page 50.)
Since operating pressure conditions are necessary for valves, however, it is necessary to clearly indicate P1 and P2when placing an order. Please indicate P2 as well when there is load resis-tance (when P2 pressure exist).
2.
In the case of the upper valve, the inlet pressure P1 is applied to the flow meter.
In that case, P1 and P2 are necessary when selecting a valve as mentioned above, and the scale of the flow meter should be the negative pressure scale (P.50) of P1.
Therefore, the pressure is controlled by a pressure regulator so that P1 will not change while us-ing a flow meter in general.
Especially, when pressure is reduced to a vacuum in the rear stage, the flow reading will be incorrect unless an upper valve type, which reduces pressure P1 so that the flow meter will not be decompressed, is used.
Care is needed.
In that case, P1 and P2 are necessary when selecting a valve as mentioned above, and the scale of the flow meter should be the negative pressure scale (P.50) of P1.
Therefore, the pressure is controlled by a pressure regulator so that P1 will not change while us-ing a flow meter in general.
Especially, when pressure is reduced to a vacuum in the rear stage, the flow reading will be incorrect unless an upper valve type, which reduces pressure P1 so that the flow meter will not be decompressed, is used.
Care is needed.
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