Posts
Controlling Cylinder Speed
| 4-Way | 4 Flow Directions |
| 2 - Position | Actuated/at rest |
| Normally Passing Classification | Not Applicable |
| Push Button, Spring Return | Operator Type |
| 5 Ports | 1, 2, 3, 4, and 5 |
Each cylinder port has its own exhaust
Standard labels apply --- ISO standard shown above, may also be:
Sandwich Speed Control
NOTE:
- Dotted line indicates an assembly --- a modular combination of devices; in this case a valve and a speed control sandwich.
- Metering devices are needle valves and serve to restrict only the exhaust --- supply is full flow.
- Modular design allows control from the valve (often the cylinder is inaccessible or in a protected cell).
- Only by restricting both exhaust flow paths can we extend and retract at the same speed.
Controlling Cylinder Force
NOTE:
- Dotted line indicates an assembly---a modular combination of devices; in this case a valve and a double regulator sandwich.
- Observe that the addition of the sandwich regulator has altered the valve flow paths. IMPORTANT!
- Modular design allows control from the valve's location.
- A direct acting multi-purpose valve can have supply and even different pressures at ports other than 1 or P---achieving different functions.
Vacuum Cap
Objective: Vacuum cup picks up part/part blow off
NOTE:
- Valve in "12" condition has vacuum at the cup and regulated air fills a small volume chamber.
- Valve in "14" condition has vacuum blocked and a puff of air breaks the vacuum lock and blows off the part. Force is adjustable. Volume chamber sized for volume required by the circuit.
- Valve selected to maintain position in the event of power failure --- double solenoid detent also only requires momentary pulse of electricity.
- Single valve solution/saves energy/fail safe/adjustable.
Cylinder Deceleration
Objective: Cylinder Decel Circuit or Varying Clamp Force
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- Cylinder extends and retracts with signal to main valve.
- Pressure to main valve controlled by selector valve.
- Cylinder can extend, then, with higher pressure selected, clamp with greater force.
- Varying selected pressures can decelerate/accelerate the cylinder.
OBSERVE:
Cylinder will not stop until the back pressure rises high enough to balance the forces on the piston --- analysis follow.
NOTE:
- Air is trapped in the cylinder. Any leakage (fittings, piston seal, rod seal, valve) will allow the cylinder to move or drift.
- When air is exhausted by a lockout or dump valve, air will be trapped in cylinder.
- If load is vertical --- any cylinder lines' inadvertent exhaust will cause the load to drop unexpectedly.
- During start up --- the all ports blocked center valve does not allow the air to pressurize the cylinder. First stroke could be at high speed due to potential lack of air at either end of cylinder.
- Disconnecting any air lines for maintenance may cause unexpected rapid movement of the cylinder --- even if OSHA lock out has been correctly actuated.
Three Position Valve 2
NOTE:
- Check valves stop and hold cylinder in mid position.
- Regulators balance pressures.
- In case of electrical failure, valve defaults to mid position, and the check valves stop and maintain cylinder position.
- In case of pneumatic supply failure, valve defaults to mid position, and the check valves stop and maintain cylinder position.
- During start up, first cycle does not cause rapid cylinder motion.
- Be aware, however, air will be trapped even if a lock out valve is opened upstream of this valve.