Pressure valve
A pressure valve is used in hydraulics or pneumatics to regulate or limit a pressure or to switch depending on a signal pressure. There are different types of pressure valves.
Pressure relief valve
The pressure relief valve is also referred to as a safety valve or pressure relief valve (short: DBV ). This valve is used to limit the maximum permissible hydraulic or gas pressure in order to protect the pressure system against excessive pressure (overpressure protection) and to avoid damage. If the pressure in the system exceeds a desired (set) value, this valve allows the medium to drain to the tank or to the outside. As a rule, the maximum pump pressure is secured against being exceeded with such a valve.
Pressure reducing valve
→ Main article: pressure reducer
The pressure reducing valve reduces the pressure existing in a system to a set value. The pressure upstream of this valve is determined by the pressure relief valve, the pressure downstream of this valve (pressure reducing valve) assumes the set (lower) pressure.
This valve is used to supply part of the pressure system with a lower pressure than is done by the pressure relief valve.
Pressure switching valve
The pressure switching valve, also called a pressure sequence valve or sequence valve, blocks a line until the pressure set on this valve is reached. When the set pressure is reached, this valve opens and the medium (liquid or gas) flows unhindered through the valve.
This valve is used to supply a part of the pressure system with pressure only when a certain, set pressure has been reached at another point in the pressure system.
Example: Functional sequence for a tool clamping device
Standardized hydraulic circuit symbols are used to represent hydraulic systems.
The pump (P) conveys the medium (the hydraulic fluid) from the tank via the solenoid valve MV2 (P to A). It flows back to the tank, no pressure builds up in the system.
If solenoid valves MV1 and MV2 are now switched, the medium arrives
- via MV2 (P to B) to the pressure reducing valve DR (P to A) and from there to cylinder 2 as well
- Via MV1 (P to B) also to the pressure sequence valve DZ, port P. The pressure sequence valve DZ remains closed because there is still insufficient pressure at port X.
The pressure reducing valve DR is set to 120 bar and is still inoperative because the pressure has not yet built up that high.
The medium flows to cylinder 2 and this extends against spring force until it comes up against an external resistance (e.g. workpiece that is to be clamped). Now the pressure continues to build up in the system. Once the set pressure of the pressure connection valve DZ has been reached (for example 100 bar = minimum required clamping pressure), it opens so that the medium in the connection valve DZ flows from P to T and thus advances cylinder 1.
Valve DZ ensures that the clamping pressure does not drop below the set value of 100 bar.
On the other hand, valve DR reduces the maximum pressure that can be achieved in the clamping cylinder 2 to the set value (for example 120 bar) so that the workpiece cannot be damaged by the clamping cylinder.
If cylinder 1 has reached the end position or if it encounters resistance, the system pressure would increase (unlimited!). The pressure relief valve DB is required so that an inadmissibly high value is not reached here. This ensures that the maximum achievable pressure does not exceed the 200 bar set there.
In this case (unforeseen resistance at cylinder 1) the system pressure would reach 200 bar, but the clamping pressure would be reduced by the valve DR to the 120 bar set there.
When the process is finished, the two solenoid valves MV1 and MV2 switch to the starting position and both cylinders retract.