Does anyone know of an inexpensive method of automatically turning on a small 120VAC load for a couple minutes once a week or so?
The application is an automatic water drain for an air compressor. I want to install a solenoid valve at the bottom of the tank, and turn it on once a week or so to drain out the accumulated water. The exact time of day that it actuates isn't important, and neither is the exact frequency of operation. A standard intermatic type time switch gives a minimum "ON" cycle time of 15 minutes, which is much longer than needed to blow out the water, and would waste a lot of air. I have seen digital programmable devices, but they seem like overkill for this application, with mulitple outputs and setpoints which I would never need. Time switches would also need to be reset after a power interruption, which is annoying. I am thinking of something like a time delay relay with a repeat cycle mode, but I don't know of any with such a long cycle time.
Yes, I know that there are automatic float type valves that are made just for this purpose, but we have tried several models, and they all failed shortly after installation. A solenoid valve/timer should be a lot more robust, since it isn't relying on floats which tend to bind up over time.
[This message has been edited by NJwirenut (edited 09-02-2006).]
I think I know what you are looking for NJWirenut, my firehouse has the same thing on our compressor but it fires once every half hour or so for about a second. I will take a look at what is running it later today and post back.
Re: Very low duty cycle timer?#69224 09/02/0601:34 PM09/02/0601:34 PM
harbor freight sells an automatic tank drainer that is hooked up through the unloader line on the pressure switch.it empties when it comes on & when it shuts down. works pretty good. has every thing ya need in the box.some of the supply houses should have these.
Re: Very low duty cycle timer?#69225 09/02/0602:45 PM09/02/0602:45 PM
NJ, If you follow your 24 Hr />=15 min timer with any of a number of "interval on" timers, your final result would be a shorter purge every day. You could fine tune the combination any way you wanted. Joe
Re: Very low duty cycle timer?#69228 09/03/0610:26 AM09/03/0610:26 AM
They make automatic drain valves for just this pupose. If you contact an air compressor supplier or visit their web site you should find one. Here's a link to one that is similar to those that I've used in the past. They're available in all voltages. The ones that I've used typically come equiped with a 110v cord. http://www.generalairproducts.com/pages2/drainvlvs.html
Re: Very low duty cycle timer?#69230 09/03/0612:28 PM09/03/0612:28 PM