In hydraulic systems, hydraulic energy is produced as there is a prime mover, generally an electric motor, driving the pump. This develops hydraulic pressure due to resistance to the flow of the pump. However, if the pump flow is off-loaded, recirculated back to the tank, or brought to a stop during the circuit’s non-action periods, the hydraulic system gets damaged. These non-action periods happen during time-delay periods of the sequence of the circuit, the end of the circuit sequence or the stroke, or actuator delay.
How to avoid damage in the hydraulic system?
Circuit designers utilise cleverly-designed systems to control the pump flow and maximum system pressure during non-action periods, so as to avoid overheating of the hydraulic fluid, power wastage, and hydraulic system damage. Through the use of a pressure control valve, the actuator force is controlled, and pressure levels are determined. Here are other system functions of pressure controls:
- Assist actuators’ sequential operation in a circuit
- Limit maximum system pressure at safe levels
- Reduce pressure levels from the main circuit to a lower pressure
- Regulate or reduce pressure in specific portions of the circuit
- Unload system pressure
How do various types of pressure control valve work in hydraulic systems?
There are four different types of valves, and their identifications are based on their functions in the circuit.
Counterbalance valve protects the hydraulic system from line failure, pressure shocks, enables free flow in one direction, and many other functions.
Pressure-relief valve limits the ceiling pressure in a hydraulic circuit by creating an alternate path for fluid flow when preset pressure level is reached. It protects the system from having excess pressure as what is required in all fixed-volume pump circuits. Relief valves are important when actuators stall with the still-in-shifted-position directional valves.
Relief valves can be compared to a fuse in an electrical system. It protects the system from the excess current by keeping it below the preset level.
Utilised in maintaining reduced pressures in parts of hydraulic systems, the pressure-reducing valves are actuated by the pressure flowing downstream that tends to close as it reaches valve setting. They usually come with a check valve to enable reverse free flow.
The unloading valve is used to dump excess fluid to the tank, with little to no pressure. It is usually applied in high-low pump circuits, where there are two pumps that move an actuator at low pressure and high speed. This lets the circuit shift to a single pump, giving off high pressure to do the work.
Unloading valves also function in sending excess flow coming from a retracted oversize-rod cylinder’s cap end to the tank. A smaller and less-expensive directional control valve can be used in this process while keeping a low-pressure drop.
If you think we missed to cite some other types of pressure control valve, comment down below.