help with a delay off timer for air compressor safety

I want to put a maximum run timer on my air compressor. It already uses a magnetic starter and a standard mechanical pressure switch for air pressure. What is the simplest way to install a timer that will turn the compressor off if it blows a hose (say, over 10 or 15 minutes run time), but will allow the compressor to cycle normally? Wiring through a light switch isn't an option, as the air is frequently used outside when the building is not occupied. I'm ok with having to cycle a disconnect in the event the timer locks out.

How about a second pressure switch set pretty low and a little away from the tank, this would be set to close if pressure drop in the line indicated a broken line and it would then close a solenoid valve on the line.
Better would be some kind of flow switch to close contacts at or above a certain amount of flow, I dont know offhand what that would be.

I think a digital timer could do what you are asking, it would just be set for your 10 or 15 minutes and every time the pump runs it starts to count down, most or all of the time the pressure switch will shut it off but if it does not then the countdown timer would. It would be best if you would need to manually reset the system.

I have been wanting to do something similar on my water pressure pump (booster pump), a timer would not work for me since pump needs to run for long periods of time to irrigate in the summer.
If the tank runs dry then the pump does not like it. Easy way is just a low level float switch in the tank...

What's the longest cycle the compressor ever runs, like when sand blasting?
I can't think of an 'easy' way to do that without at least a smart relay if not a PLC. Maybe all you need is a time delay relay. Someone will come on here and explain the simple solution.

Check into timers used in HVAC. Mostly they are minimum off time units, but I think there are also run time limiters.

Run time limit timers for HVAC - Google Search

3 phase motor?
440-220-110?
Coil voltage on the starter?
You stated that a total power shutdown is OK to recycle, that makes things easier.
Bob

240V holding coil, high leg delta.

A basic timer with changeover contacts that energizes after a certain time will do. Wire it so the input power is taken from after the pressure switch.

Use the COM+NC contact to disconnect the contactor coil once the timer times out.

An NC pushbutton will work as a reset, or just bridge it out and use the disconnect. The shown position means you can reset the timer without stopping the compressor.

Example schematic:

The timer will need to have 240V-rated contacts and a 240V coil. Something like this: Blocked

A interval timer wired in series with the mag would time out after its programmed time elapsed and drop the compressor out. That programmed time must be longer than any anticipated run time for the compressor during heavy use, such as sandblasting.

This is what I'm thinking of...88827145 Crouzet | Crouzet SPDT Interval Timer Relay, 0.1 s → 100 h, 1 Contacts, 24 → 240 V ac, 24 V dc - SPDT Switch | 774-0314 | RS Components

Stuart

Depending upon the size of the air compressor it may in fact continue to pump air and even cycle with a blown hose.
We have both large recep and rotary screw compressors and we could chop off the end of a 3/8" air hose and the compressors will actually charge and cycle . Not trying to complicate things, how about some simple quarter turn ball valve that is turned off inside at the end of the day and one outside with a simple sign "please turn valve on for air and off after use" outside.

dana gear said:

Depending upon the size of the air compressor it may in fact continue to pump air and even cycle with a blown hose.
We have both large recep and rotary screw compressors and we could chop off the end of a 3/8" air hose and the compressors will actually charge and cycle . Not trying to complicate things, how about some simple quarter turn ball valve that is turned off inside at the end of the day and one outside with a simple sign "please turn valve on for air and off after use" outside.

Click to expand...

Oh, totally. 3" air lines exist for a reason.

Another option is to do the light switch or motion sensor inside, and just have a 'push for two hours' button outside.

These are used to save well pumps and may work for this, however if as stated above the compressor is big enough that it can overcome the leak it won't.

https://www.homedepot.com/p/Square-...he switch works with a,will turn off the pump.

SomeoneSomewhere said:

A basic timer with changeover contacts that energizes after a certain time will do...

Click to expand...

That's exactly what i would do... and the theory is simple:

You're looking specifically for an "out of normal range" cutoff circuit.

You use a pressure switch to detect an extreme low pressure (like... lower than your minimum operating pressure would ever fall...) and an adjustable timer (set to some arbitrary value at first, but trimmed-to-suit) where:

A) you would expect the compressor to be able to bring up system pressure beyond your switch's setpoint well within the timer's timeframe

B) NOT want the compressor to run beyond that timeframe, below that pressure.

Example:

You have your shop compressor set to 150psi, and regulated to 110. Compressor pressure switch kicks on at 120, off at 150. Your heaviest load is a bead-blasting cabinet regulated to 90psi, and when using it, your system compressor will be at 100% operation after using the cabinet for 4 minutes, at which time, your system pressure will continue to fall, and at 8 minutes, your cabinet's nozzle pressure will fall below 90%, at which time you stop and wait it out.

Using it in this fashion, 40psi at your TANK will NEVER appear in 'normal operation'. A severed hose, or blown off end connector would pull your system down beyond that 40psi point.

SO... let's say a 40psi switch establishes your 'cutoff pressure'

Next... Let's say that when your compressor starts from a 'zero pressure' state, it takes 40 seconds to bring your system pressure above 40psi.

Set your cutoff timer for 60 seconds.

This allows the system to start from full discharge, and bring up pressure beyind the minimum cutoff before the timer expires.

Wire the switch in N.C. mode (no pressure = closed contacts), and set for 40psi
Wire the relay for a Delay On mode (an ICM 102 is perfect for this!) and set for 1 minute.

Connect this circuit in series with the coil of a relay whose N.C. contact is in series with the compressor's motor contactor coil.

When you energize the system, the timer starts. IF pressure doesn't exceed 40psi in 60 seconds, the compressor motor contactor coil will de-energize.

This circuit will continue to hold the motor in a 'shut off' state until you force a manual reset (cycle the power).

If you want the system to automatically 'retry' on regular intervals, a clock timer on 15 minute intervals could be used to re-trigger the timer.

I prefer to have mine shutdown and 'not' restart'... I reserve auto-retry for only seriously critical stuff, where a retry is a last-ditch effort to restore a service which may be affected by some transient circumstance. A broken hose, once broken, stays broken until repaired...