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Frequently Asked Questions
How is the delay actually produced?
By filling a known volume through a known restriction. Air passes the needle valve into the reservoir, pressure rises along a curve set by the two, and the pilot section trips when it reaches its threshold. Widening the needle valve shortens the fill and therefore the delay, which is why the adjustment is continuous rather than stepped.
When does a circuit need off-delay rather than on-delay?
An on-delay timer waits after the input arrives before switching its output, which is how a dwell before the next motion is created. An off-delay timer switches immediately with the input and then holds the output for the set time after the input goes away, which is how a blow-off or a clamp release is extended past the signal. The internal check valve orientation is what distinguishes them.
How repeatable is a pneumatic delay?
Good enough for sequencing, not good enough for measurement. Air viscosity changes with temperature, so the same setting runs longer on a cold morning than on a hot afternoon, and supply pressure variation moves the trip point. Where a few percent matters, the timer is usually replaced by a position sensor confirming the motion has finished.
Why use one at all when a PLC timer is more accurate?
Because there is no PLC, or because electricity is unwelcome. A stand-alone jig, a manually loaded fixture or a portable rig can be sequenced entirely in air, and in explosive atmospheres a pneumatic circuit avoids the certification, wiring and inspection an electrical timer would bring with it.
Can the range be extended beyond what the adjustment gives?
Yes, by adding an external reservoir to the timing port. The timing volume and the restriction multiply together, so a larger reservoir shifts the whole adjustable band longer. Manufacturers publish which port to tap and the reservoir sizes that correspond to the extended ranges.
Why has a timer that was set correctly started drifting?
Usually contamination in the needle valve. The timing orifice is deliberately small, so a trace of oil, sealant or fine particulate changes the flow through it and therefore the time - and it drifts in one direction rather than scattering. Clean, dry air ahead of the timer keeps the setting where it was left.
Does the timer need to be reset between cycles?
The timing volume has to bleed back down before the next delay is repeatable. Most units exhaust the reservoir automatically when the input is removed, but a cycle that re-triggers before the exhaust completes gives a short second delay. Where cycles run fast, the reset time has to be checked against the cycle time.