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#69221 - 09/02/06 09:44 AM Very low duty cycle timer?
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
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).]

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#69222 - 09/02/06 09:58 AM Re: Very low duty cycle timer?
Tiger Offline
Member

Registered: 05/04/05
Posts: 714
Loc: Crystal Lake, IL USA
Isn't there a small tank & pump used in HVAC to pump whatever drips out of furnace/a.c. units?

Dave

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#69223 - 09/02/06 10:17 AM Re: Very low duty cycle timer?
JCooper Offline
Member

Registered: 12/30/02
Posts: 229
Loc: Kendall Park, NJ USA
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.

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#69224 - 09/02/06 10:34 AM Re: Very low duty cycle timer?
circuit man Offline
Member

Registered: 11/05/01
Posts: 287
Loc: saluda,s.c.
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.

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#69225 - 09/02/06 11:45 AM Re: Very low duty cycle timer?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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).]
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#69226 - 09/02/06 01:57 PM Re: Very low duty cycle timer?
CharlieK Offline
Member

Registered: 03/10/03
Posts: 23
Loc: Baltimore. Md. U.S.A.
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

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#69227 - 09/02/06 03:46 PM Re: Very low duty cycle timer?
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
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

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#69228 - 09/03/06 07:26 AM Re: Very low duty cycle timer?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#69229 - 09/03/06 09:11 AM Re: Very low duty cycle timer?
Helectric Offline
Member

Registered: 01/07/05
Posts: 91
Loc: Brandon, SD
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

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#69230 - 09/03/06 09:28 AM Re: Very low duty cycle timer?
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
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!

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