Description
Shako VSS Soft Start & Dump Valve 1/4"-1/2"
The SHAKO VSS Series soft start and dump valve provides controlled pressurisation and automatic exhaust of pneumatic systems, helping protect machinery, pneumatic components and personnel from sudden movement when compressed air is initially applied.
Available in 1/4", 3/8" and 1/2", the VSS gradually introduces compressed air into the downstream pneumatic circuit during start-up. Once downstream pressure reaches approximately 50% of the inlet pressure, the valve switches to full-flow operation.
When the solenoid is de-energised, the inlet supply is shut off and downstream compressed air is automatically exhausted through the 3/8" dump port, allowing residual system pressure to be released.
Soft Start Operation
When the solenoid valve is energised, incoming compressed air initially passes through an adjustable internal throttle.
This allows downstream pressure to increase progressively rather than applying full line pressure instantaneously.
When outlet pressure reaches approximately 50% of the inlet pressure, the internal mechanism changes over and allows full flow through the valve.
The soft-start function can help:
✓ Reduce sudden cylinder movement
✓ Reduce pneumatic shock
✓ Protect downstream components
✓ Provide controlled machine start-up
✓ Improve pneumatic system safety
Automatic Dump Function
When electrical power to the solenoid is removed, the VSS automatically:
✓ Closes the compressed air inlet
✓ Isolates the upstream air supply
✓ Opens the downstream exhaust path
✓ Releases residual system pressure
Downstream air is exhausted through the integrated Rc 3/8" exhaust connection, allowing machinery and pneumatic circuits to depressurise following shutdown.
Valve Specification
Function: Soft start + dump valve
Operation: Solenoid controlled
Media: Compressed air
Port sizes: 1/4", 3/8" or 1/2"
Threads: BSP as standard
Optional thread: NPT
Exhaust port: Rc 3/8"
Operating pressure: 0.25–9 Bar approx.
Proof pressure: 15 Bar approx.
Ambient temperature: -10°C to +60°C
Duty cycle: 100% ED
Mounting: With or without bracket
Body: Aluminium alloy
Available Models
VSS-02 – 1/4"
VSS-03 – 3/8"
VSS-04 – 1/2"
BSP connections are standard, with NPT available as an option.
Solenoid Coil & Electrical
Standard coil: DIN connection
Power: 4.5W
Duty rating: 100% ED
Insulation: Class F
Protection: IP65 with connector
Standard voltages include:
✓ 24VDC
✓ 110VAC
✓ 230VAC
Additional AC and DC voltages can be supplied according to application requirements.
Optional ATEX Solenoid Operator
For hazardous-area applications, the VSS can be supplied with a compatible Nass Magnet explosion-protected solenoid operator.
Typical protection includes:
Ex mb IIC T4 Gb
Ex mb tb IIIC T130°C Db
Suitable for appropriately specified gas and dust hazardous-area applications.
Adjustable Soft Start
The rate at which downstream pressure initially increases can be adjusted using the valve's internal throttle control.
This allows the start-up characteristics to be matched to the pneumatic system, helping prevent cylinders and actuators from moving abruptly when compressed air is restored.
Once sufficient downstream pressure has developed, the valve automatically changes to its normal full-flow condition.
Typical Applications
✓ Pneumatic machinery
✓ Automated production equipment
✓ Cylinder control systems
✓ Machine start-up circuits
✓ Pneumatic safety circuits
✓ Packaging machinery
✓ Assembly equipment
✓ OEM pneumatic systems
✓ Industrial compressed air systems
✓ Automated process equipment
Why Use a Soft Start & Dump Valve?
Restoring full compressed-air pressure instantaneously to a depressurised machine can cause cylinders and other pneumatic actuators to move suddenly.
The VSS provides a controlled initial pressure increase before automatically switching to normal flow.
When the solenoid is switched off, the process is reversed: the incoming air supply is isolated and downstream pressure is exhausted, providing a convenient combined soft-start and dump function in a single valve assembly.
Important Safety Note
Although a soft start and dump valve can form part of a machine's pneumatic safety system, suitability for a particular safety function depends upon the complete machine design and required safety performance.
Where compliance with a specific machinery safety standard or Performance Level is required, the complete pneumatic safety circuit should be appropriately designed and validated.
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