Dual sump pumps-check valve?

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On 11/20/2011 8:23 AM, snipped-for-privacy@optonline.net wrote:

bs. where does this alleged "air" come from?
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Steve Barker
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You claim it's BS, yet others have given cites here back to sump pump manufacturers that call for putting that small hole in the discharge line. I just installed one last week that also called for the hole in the instructions.
As I already explained, the air in the pipe comes from the water between the check valve and the sump pit water level draining back into the sump when the pump shuts off. The check valve only prevents the water in the rest of the discharge line from flowing back.
So now you have a section of pipe full of air. Worst case, if the basin is dry, there is no water at all and it's initially all air in the pump and pipe. As the sump basin fills, without a check valve that air would be displaced and the pump and pipe would fill with water too. The water level inside and outside the discharge line would be equal. With the check valve, that air remains trapped and it can stay there, air locking the pump. Meaning the pump impeller remains mostly or entirely surrounded by air, unable to move water.
That is the purpose for drilling a small hole in the discharge line near where it connects with the pump. With the hole, the water level inside the pump and pipe will be equal to the water level outside. And that way you are sure that the pump cannot airlock.
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On Mon, 21 Nov 2011 04:44:59 -0800 (PST), " snipped-for-privacy@optonline.net"

I thought this was BS too until I read up on it. What you say all makes sense. So I won't argue against the pump experts, just make a few comments. If a pump is primed, there is no air at the impeller. If the sump is dry the pump isn't primed and there's air around the impeller.
Where does the air come from? All the water has drained out, simple as that. The water between the pump and the check valve gurgles down, so the pump is full of air. As the sump fills, the pump head fills with water, priming it. Air in the discharge line can stop the water from filling the pump head if the air compresses because it can't escape. Then you have pump airlock if the pump goes on.
Here's where it gets a little tricky, and what fooled me. How much head pressure does it take to overcome the air blockage? I've got 2 pumps with check valves and no drilled relief holes. Pumps always work fine. Now some pumps have that relief hole built into the head. I don't know if mine do or not.
The check valves I put in have light rubber flaps. Wouldn't take much pressure on the underside to unseat them. Then the pump head will prime. Back to head pressure. Some pumps kick on before there's much head pressure, others wait until there's more water in the sump. A float switch can be set to adjust that. Both of my pumps have diaphragm switches with no adjustment. I've noticed they don't go on until almost the entire pump is covered with water.
Anyway, though my pumps aren't getting airlocked, what if the rubber on the check valve take a real good seat, and sticks a bit? I could get airlock. So when I get around to it I'm going to drill the relief holes.
--Vic
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On 11/21/2011 6:22 AM, Vic Smith wrote:

Ok, that makes sense. I had not considered the sump that is dry at times. The ones i have, have always had water in them 365 days a year. I rekon i can see what you said happening in one that has dry times.
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wrote:

Ah! The light dawns. You are correct. If the sump ever drys below the impellor level it could air lock.
I also drill the holes when the manual calls for it.
Harry K
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And why would it "air lock" even without the hole? The pump is going to push water up the pipe, compress the air which will push open the checkvalve, push on he water above the checkvalve and the entire system works just as it would as if there were no air in the system. As long as the check is above the pump rotor it cannot air lock.
Harry K
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On 11/20/2011 7:43 AM, Joe J wrote:

yes, $4 or $5 well spent especially if you have a small sump.
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"Dual sump pumps - check valve?
In the same crock I have two sump pumps on two separate breakers. "
It's one of the clearest posts I've seen.

" I had a failure on the primary pump and it seemed half the crock was refilled by the remnants in the pipe draining back after the backup pump shut off. "
That's why.

To correct the misinformation.

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On Sun, 20 Nov 2011 07:27:31 -0800 (PST), " snipped-for-privacy@optonline.net"

The three we have for a pit at work? They are actually part of a water system and pump the water from a pit to a cooling tower and are mounted at ground level. Thus the need for a foot valve. They draw from a pit that is about 5' deep and pump to the tower that sits about 20' above ground level outside the building.
OTOH, you are correct about the typical sump pump application used in basements. They are best right inside the pit and operated with a float switch.
We do have a sump pump that has a check valve in line. The check is needed because it is connected to a common line that other pumps are connected to that go to the sewer. This is more in line with the setup the OP is talking about. With no check valve, water will go back to the other pump in line. IMO, the OP needs a check valve in line after the pump.
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Exactly and I figured that is what we are talking about since it's a home repair group and nothing indicated there was anything exceptional about the situation. And everything since then shows that was correct.

I'd probably put one in too. I would definitely put one in if it were the main pump. Being a backup, the fact that some of the water will flow back in isn't as much of an issue because it's not going to be happening frequently, only if the main pump fails. So, if the pump cycles a bit more, it's not a big deal.
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On Nov 20, 9:25 am, "Stormin Mormon"

Andy answers: A question of terminology..... Both do the same thing --- a valve that allows matter to flow in one direction. In my experience, a "foot" valve is often mated with a screen and a "check" valve is simply inserted in-line... If JoeJ's pumps are both submersible, I can't see where either could be used..... Perhaps I am missing something, since the submersibles I have used don't have a convenient place to add either one......
I'd be happy to get information on my error.....
Andy in Eureka, Texas PE
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On 11/20/2011 7:39 AM, Andy wrote:

it is installed on the discharge side to prevent the contents of the riser pipe from dumping back into the sump. And no, a foot valve is not the same as a checkvalve on the discharge side. A foot valve is used on the suction side and IS in fact there to keep the pump primed, in the case of a well pump (or any other pump for that matter) that is above the water line.
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On 11/20/2011 7:18 AM, Andy wrote:

the check VALVE is NOT there to keep the pump primed in the case of a sump pump.
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One reason I can think of is to save a few $$, because the backup will rarely, if ever, be used. And the only downside to not having a check valve is that some water will run back in. For an installation where the pump only runs occasionally, it's a backup, etc and not that much water runs back in, it's not an issue.
Other reason would be if water that would be held in place by a check valve is subject to freezing. Then it would be relying on water being able to drain back to prevent freezing.
I had a failure on the primary pump and it seemed half

How much water runs back in is determined by how much pipe there is that is left filled with water when the pump shuts off. In your case it sounds like it's substantial amount.

The closer it is to the pump the less water will flow back. Height isn't an issue. Usually it's put above the sump pit for convenience. If a lot of water flows back, then yes it would make sense to put one in to keep the pump from going on and off more frequently.

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On 11/20/2011 7:23 AM, snipped-for-privacy@optonline.net wrote:

ACTUALLY, the are usually threaded and screwed directly into the pump. Then the pvc attached to the checkvalve.
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in a typical installation there would be a union beneath the check valve for easy replacement and trader it it on the head the check valve prevents the discharge water in the pipe from refilling the sump

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Joe J wrote:

Hi, Our house does not have water problem but I installed check valve in the main sewer line. It is good safety feature. Very unlikely but worst case your two pump can fight each other.
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wrote:

Think he said they are on separate discharge lines, so they won't fight. The check valve will prevent pumping the same water twice.
When I added the second pump to my pit with a Y I brain-farted with the check valves and had to redo it. One pump would backfeed through the other. Putting a check valve over each pump discharge fixed it.
--Vic
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Yes, two separate lines. One underground to the sewer, the other, out of the side of the house and on the lawn.
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On 11/20/2011 7:10 AM, Joe J wrote:

it all depends on the size of the 'crock' as you call it. If the sump is of sufficient size, then you can get away without a check. But having said that, it is standard procedure to put a check on the pump down low. (like screwed into the pump, then the discharge pipe connnects to it.)
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