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).]

Isn't there a small tank & pump used in HVAC to pump whatever drips out of furnace/a.c. units?

Dave

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.

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.

I have used these electric auto drains with good success.



They did not clog up in a very damp and dirty environment.

If you must build your own I know timers that will work but they are not inexpensive. $100 - $200.



[This message has been edited by iwire (edited 09-02-2006).]

NJ. try a Intermatic C8855. It has an on renge of 21/2 seconds to 5 minutes every 24 hours and sells for about 100.00

Charlie

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

Joe brings up a good point about the timing.

A few seconds a day is IMO a better idea than once a week.

The electric one I posted above we might even set for 1 or 2 seconds per hour.

A quick PSSHHHHT every hour and the tank stays dry.

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

Looks like McMaster-Carr carries the one Iwire posted. Will probably order one of those.

Hopefully the electric setup will hold up better than the float type.

Thanks, all!

Here are two links to possible solid state solutions to the problem. One is the datasheet to the LS7210 digital delay timer. The other is to an application note the describes delays from a day to over a year. These will mainly be of interest to techies among us.
Joe http://www.lsicsi.com/pdfs/App_Notes/AN1002.pdf
http://www.lsicsi.com/pdfs/Data_Sheets/LS7210.pdf

Looks like you probably have enough info already but since I'm back in the office today and have it handy I'll send you this anyway. Here's a link to the one that we use. It's made by Deltec just for air compressor filters and we've had very good luck with them.
http://www.deltech-flair.com/support_files/pdf_files/SalesLit/ADVsalesLit.PDF#search='deltech%20automatic%20drain%20valve'