Operate 2-way flow regulator
1- The flow limiter
The flow rate in a limiter of flow varies according to the pressure difference across it (Bernoulli's theorem).
Q = K*S*√?P
Q : flow.
K : form factor of the flow limiter.
S : passage section of the flow limiter.
The terms flow reducers, flow restrictors correspond to the same component. (Symbol below).
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Figure (A) shows a bidirectional flow restrictor. That is, the flow is reduced in both directions of passage.
Figure (B) shows a unidirectional flow restrictor. That is, the flow is reduced only in one direction. In the other direction, a part of the flow passes through the restriction and the other part through the non-return valve.
2- Flow regulator
The flow regulator keeps a constant flow regardless of the load of the receiver.
There are two types of flow regulator:
- 2-way flow regulator.
We can find ourselves two symbols:
- The detailed symbol (Fig. 1).
- The simplified symbol (Fig. 2).
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3- Flow regulator: closed valve
The diagram is representative of the mechanics. In the figure above, the pressure balance of the flow regulator consists of a spring (item 5) determined by the manufacturer which is between 2 and 10 bars. The spool (item 6) is normally open at rest. It will close when the pilot pressure (item 7) will counteract the spring force (item 5) which is added to the pressure of the load of the receiver brought by the pilot (item 8). A jet on the control pilot (item 8) makes it possible to stabilize the pressure balance.
The pressure balance works on the principle of pressure reduction. Its role will be to maintain a constant pressure difference across the restriction (item 9).
The restriction (item 9) is completely closed. The pump (item 1) driven by a heat engine (item 2) delivers a flow rate of 30l / min. The flow accumulates at the level of the restriction, the pilot pressure instantly reaches the displacement pressure of the spool (item 6) and closes the passage of the oil. The oil from the pump returns to the tank via the pressure relief valve (item 3).
We see a pressure of 200 bars in M1 and 5 bars in M2 (stand-by pressure).
4- Flow regulator: cylinder output
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When the restriction of the flow regulator is opened, the 5 stand-by bars return to the spring (item 5) and open the pressure balance. The cylinder leaves at a reduced speed under a pressure of 50 bars in M3. A flow of 10 l / min passes through the regulator, the excess flow (20 l / min) returns to the tank by the pressure relief valve (item 3) under 200 bars. The pressure balance reduces the pressure from 200 bars to 55 bars in M2. (50 bars of load + 5 bars of spring). It allows only the bit rate requested by the restriction.
There is a pressure difference (ΔP) of 5 bars across the restriction.
5- Flow regulator: cylinder output with load change
During the output of the cylinder rod, the load increases from 50 to 100 bars. The pressure returned to the spring of the pressure balance (item 5) increases to 100 bars, which causes a slight movement of the spool (item 6) down. By adding slightly more oil at the restriction, the pressure rises to 105 bars in M2. The excess flow returns to the tank by the pressure relief valve (item 3) under 200 bars.
It can be seen that the pressure difference across the restriction is always 5 bars. The flow will remain unchanged and the cylinder will come out at the same speed.
6- Flow regulator: cylinder in mechanical stop
The cylinder reaches mechanical stop. The pressure in the circuit instantly rises to 200 bars in M1, M2 and M3. The pressure balance is fully open.
It can be seen that the (ΔP) across the restriction is 0 bar. No flow goes into the flow regulator.
The entire pump flow (30 l / min) returns to the tank via the pressure relief valve (item 3).
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