ESV@psuvm.psu.edu (ANDREW COLL esv@psuvm.psu.edu) (09/14/90)
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, it pumps water
from both basement sinks of a duplex house, 4 feet up into the stack.
There is a check valve on the pump outlet to prevent wastewater from
the stack from entering the pump and so on. My problem is this:
The pump is supposed to come on automatically, via a float switch on
the inlet pipe, one foot away from the pump. When water flows into
the pipe, the float switch turns on and starts the pump. The pump then
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.
This can't be terribly good for the lifetime of the pump and no amount
of adjusting float switch will correct the problem. Moving the switch
farther away from the pump is impractical because the plumbing in this
house is at least 40+ years old and its far more likely that I'll break
something if I try to modify the drain system.
My only idea so far was to use the float switch to trigger a 555 timer
set up as a retriggerable one-shot with a variable duration between
30 seconds and 5 minutes (whatever I find works best). I would probably
operate the motor with relay driven by a power transistor. My questions
are: 1. Does this sound reasonable and 2. Should I use the relay
or opt for some kind of SCR based circuit to operate the motor and
3. Does anyone have a better idea? :-)
Many thanks....
Andrew Coll ESV@PSUVM.BITNET
ESV@PSUVM.PSU.EDUhbg6@citek.mcdphx.mot.com (09/14/90)
In article <90256.174441ESV@psuvm.psu.edu> ESV@psuvm.psu.edu (ANDREW COLL esv@psuvm.psu.edu) writes: >......... When water flows into >the pipe, the float switch turns on and starts the pump. The pump then >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. Why not go buy a working switch? (or the right kind). A sump pump float switch is supposed to have two limits; a high water mark and a low one. When the water reaches the high limit, the pump turns on and pumps the 'water' out of the sump until the the lower limit is reached. The level must then rise to the high limit before the pump is turned on again. PS- Count your blessings; I learned about such things working on a SEWAGE sump pump in our house near Chicago. Stinky, messy, foul, YECH! John ..................................................................... reply to 'from' address; hbg6@citek.mcdphx.mot.com NOT the 'sender' line address! Someday my sysadm will decide this is a 'real' problem. :-) ..................................................................... All opinions expressed are mine and not Motorolas, their loss. .....................................................................
whit@milton.u.washington.edu (John Whitmore) (09/15/90)
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