Soft-Start and Progressive Start-Up Valves
A soft-start valve fills the system slowly and in stages at switch-on instead of letting full pressure hit at once. Cylinders then move into their home position under control and no one is caught out by sudden motion. This guide walks through function, switching threshold and sizing step by step.
View pneumatic valvesHow does a soft-start valve work?
At switch-on the soft-start valve throttles the incoming air through a small bypass and lets pressure rise slowly. Once the outlet pressure reaches a set threshold, usually around 50 percent of system pressure, the valve switches to full bore and releases the rated flow. Cylinders are fed gently first and move under control before the system delivers full power.
Why is a gentle start-up worth it?
Without soft-start, full pressure is present the instant you switch on. A cylinder with one exhausted chamber then slams uncontrolled into an end position, putting people at risk and stressing the mechanics. A progressive pressure build-up takes the energy out of that motion and protects seals and fittings from pressure shocks.
- Controlled cylinder motion at switch-on instead of a violent lurch.
- Protection from pressure shocks in lines, couplings and air-prep units.
- Lower load on seals for a longer service life.
- A key element for safe restart after an emergency stop or maintenance.
How do I size the valve and set the threshold?
Port size, rated flow and the air volume of the system drive the choice. An undersized valve throttles in operation and lets pressure drop; an oversized one ramps up too fast and loses the soft-start effect. Match port and flow to the air-prep unit, and let the switching threshold decide when full bore is released.
Choose a 3/2 combined valve with fast exhaust where an emergency stop is required.
Compare valvesPlace the soft-start after the filter and regulator of the air-prep unit.
To the valve overviewFrequently asked questions
Where is the soft-start valve installed in the system?
Right at the system inlet after the air-prep unit, so downstream of the filter and pressure regulator. From there it builds pressure progressively for all the pneumatics that follow.
At what pressure does the valve switch to full flow?
A threshold around 50 percent of system pressure is common. At 6 bar working pressure the valve opens full bore at about 3 bar. On many models the threshold is adjustable.
Does a soft-start valve replace a safety function?
No. It provides a gentle start and is often combined with fast exhaust, but on its own it is not a complete safety function. Safety-related requirements of the system must be assessed separately.
Find the right soft-start valve
Our pneumatics specialists help with port size, switching threshold and combining it with safe exhaust.
Vetted selection
Recommendations from maker data and system values.
Correct threshold
Switch-over point matched to the system pressure.
Safe start-up
Controlled pressure build-up protects people and mechanics.
Expert advice
Pneumatics specialists support your sizing.