What Role Does the Choke Valve Play in the Hydraulic System?

1. The main requirements of the hydraulic system for the choke valve

(1) Large flow adjustment range, and flow adjustment should be uniform.

(2) When the pressure difference between the front and rear part of the valve changes, the flow through the valve changes little to ensure the stability of the load movement.

(3) The change of oil temperature has little effect on the flow through the valve.

(4) The pressure loss of the liquid flowing through the fully open choke valve is small.

(5) When the valve port is closed, the leakage of the valve should be small.

It is conditional that the choke valve is used to adjust the flow, that is, it requires a link that accepts the pressure signal of the choke valve (relief valve or constant pressure variable pump in parallel with it). Through this link, the flow change of the choke valve is compensated.

In the hydraulic system, the choke valve and the relief valve are connected in parallel with the outlet of the hydraulic pump to form a constant pressure oil source, so that the pressure at the pump outlet is constant.

The choke valve is a component that can adjust the flow rate by changing the liquid resistance in a large range. Therefore, the flow rate into the hydraulic cylinder can be changed by adjusting the liquid resistance of the adjustable choke valve, thereby adjusting the movement speed of the hydraulic cylinder.

If there is only a choke valve in the circuit without a parallel relief valve, the choke valve cannot adjust the flow.

The hydraulic oil output by the hydraulic pump all enters the hydraulic cylinder through the choke valve. Changing the size of the choke only changes the pressure drop of the liquid flow through the choke valve.

The choke is small, the flow rate is fast; the choke is large, the flow rate is slow, and the total flow is constant, so the movement speed of the hydraulic cylinder is unchanged.

2. The choke valve usually has three basic forms

Thin-walled small holes, slender small holes and thick-walled small holes. But no matter what form the choke adopts, the relationship between the flow through the choke and the pressure difference between the front and rear part of the choke can be expressed by the formula: q=KAΔpm. The flow characteristics of the three chokes are as follows.

(1) The effect of differential pressure on flow

When the pressure difference between the two ends of the choke valve changes, the flow through it will change. Among the three structural forms of the choke, the flow through the thin-walled small hole is least affected by the change of the pressure difference.

(2) The effect of temperature on flow

Oil temperature affects oil viscosity. For slender small holes, when oil temperature changes, the flow rate will also change. For thin-walled small holes, viscosity has little effect on flow rate, so when oil temperature changes, the flow rate is basically unchanged.

(3) Blockage of the choke

The choke may be partially blocked due to impurities in the oil or due to the colloid, asphalt, etc. precipitated after the oxidation of the oil, which changes the size of the flow area of the original choke and changes the flow rate.

Especially when the opening is small, this effect is more prominent, and in severe cases, it will be completely blocked and the flow will be cut off.

The larger the flow area of the choke, the shorter the throttling channel and the larger the hydraulic diameter, the less likely it is to be blocked. Of course, the cleanliness of the oil also affects the blockage. Generally, the minimum stable flow rate of the choke valve is 0.05L/min.