Path: utzoo!attcan!uunet!know!zaphod.mps.ohio-state.edu!rpi!dali.cs.montana.edu!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Ac motor control question
Message-ID: <7612@milton.u.washington.edu>
Date: 15 Sep 90 04:23:37 GMT
References: <90256.174441ESV@psuvm.psu.edu>
Organization: University of Washington, Seattle
Lines: 26

In article <90256.174441ESV@psuvm.psu.edu> ESV@psuvm.psu.edu (ANDREW COLL esv@psuvm.psu.edu) writes:
>Greetings everyone...
>
>I just moved into a new house and had to replace a broken pump.
>I'm having a small problem controlling the motor.  The pump
>is actually a wastewater pump for a basement sink ...
>The pump sucks all of the water out of the drain line, causing the float
>switch to turn off again.  About a half a second later, enough water
>has flowed into the pipe again to turn the pump back on.  So now, the
>pump is oscillating between on and off, about fifteen times a minute.

	One way to approach the problem is to use a smaller pump; 
the 'all done' event will no longer occur so soon (but if the
sink overflows, you're sunk :-) ).  A better solution would be to put 
a standpipe on the drain line with a flapper valve and a slow
leak; if the water rises, it pushes past the flapper and raises the
float switch (installed, of course, in this pipe).  Then when the 
pump turns on and the water falls, the flapper valve closes.  Only
much later, as the leak in the flapper drains the standpipe, the switch
will turn off.
	My preference would be to homebrew the valve, but any
commercial 'check valve' can be modified (drill a hole in the
flapper) for this use.  The diameter of the standpipe and the
size of the hole in the flapper will determine the time delay.

	John Whitmore