Therefore, in order to reduce the flow resistance, there is also a valve with a reverse flow check valve. In addition to the adjustable orifice, there is also a throttle orifice that can not be adjustable, but a constant pressure differential spring pre-tightening force is adjustable. Differential Pressure Flow Characteristics Two-way flow valve differential pressure flow characteristics can be divided into three areas: Area I: The pressure difference between the two ends of the valve, p0-p2 is lower than the spring presetting pressure, and the constant pressure difference is fully open. It has a simple structure and low cost, and can be completely closed.However, with the improvement of technology, there are some needle valves that are not at all like needles: with a cylindrical spool, which has a regulation indication scale for better flow adjustment precisely. 
When the oil reverses ->, it is like a throttle valve. Set a few more values between the maximum and minimum values of the pressure adjustment range and repeat step c. Area Ill: The pressure difference is so large that the constant pressure differential valve has moved to the stroke end and it is no longer possible to maintain a constant differential. Because, at this time, due to p2
When the oil reverses ->, it is like a throttle valve. Set a few more values between the maximum and minimum values of the pressure adjustment range and repeat step c. Area Ill: The pressure difference is so large that the constant pressure differential valve has moved to the stroke end and it is no longer possible to maintain a constant differential. Because, at this time, due to p2