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Old 05-26-2011, 10:41 AM   #1
roofster
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Default sump pump relief hole

Replacing my sump pump and some of the discharge PVC. They say to drill a relief hole between check valve and pump outlet to avoid air locking the pump. As long as the hole is in the pit, should it be above or below normal water level?

Found an answer, looks like decent forum too.

http://www.selfhelpforums.com/showthread.php?t=27049

Last edited by roofster; 05-26-2011 at 10:49 AM. Reason: add link
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Old 05-26-2011, 12:17 PM   #2
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Default Re: sump pump relief hole

Quote:
Originally Posted by roofster View Post
Replacing my sump pump and some of the discharge PVC. They say to drill a relief hole between check valve and pump outlet to avoid air locking the pump. As long as the hole is in the pit, should it be above or below normal water level?

Found an answer, looks like decent forum too.

http://www.selfhelpforums.com/showthread.php?t=27049
My sump pump actually did get air lock a couple of years ago, I drilled a hole and it hasn't happened since. I drilled it below water level but I can't see how it would make a difference.
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Old 05-26-2011, 02:59 PM   #3
KCarGuy
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Default Re: sump pump relief hole

That makes no sense...then why even have a Check Valve if you bleed it off all the way to the waterline?
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Old 05-26-2011, 03:32 PM   #4
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Default Re: sump pump relief hole

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Originally Posted by KCarGuy View Post
That makes no sense...then why even have a Check Valve if you bleed it off all the way to the waterline?
kinda what i was thinking too.


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Old 05-26-2011, 03:47 PM   #5
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Default Re: sump pump relief hole

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Originally Posted by KCarGuy View Post
That makes no sense...then why even have a Check Valve if you bleed it off all the way to the waterline?
not all the way -- the hole goes bellow the check valve....
.... and my understanding was that it allows air out for the pump itself which may otherwise keep the impeller from priming up and actually pumping.
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Old 05-26-2011, 04:14 PM   #6
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Default Re: sump pump relief hole

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Originally Posted by KCarGuy View Post
That makes no sense...then why even have a Check Valve if you bleed it off all the way to the waterline?
Yeah, I know. At first glance it doesn't make sense ... but it works.

I encountered the same problem many years ago ... sump pump wouldn't pump on a reliable basis. Drilled a 3/32" hole in the discharge pipe above the water line but below the check valve and it never gave another problem.

I angled the hole down so the water spraying from the hole was directed back down into the sump.
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Old 05-26-2011, 04:46 PM   #7
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Default Re: sump pump relief hole

I have my check valve as low as possible, maybe 2 " above the discharge of the sump pump, then the hole in between that. I think my instructions called for a 3/32 hole as well. ( 1.25" discharge )
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Old 05-26-2011, 05:58 PM   #8
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Default Re: sump pump relief hole

A relief hole can be useful because it allows the pump to purge entrapped air, but its usually only really needed for the first initial priming of the pump. If your pump continually loses prime, then the root problem may be setting the "off" float position too low.

PS - it will work best if located above the water line
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Old 05-26-2011, 06:01 PM   #9
Frank The Plumber
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Default Re: sump pump relief hole

The answer to this is found in fluid hydraulics.

You are not drilling a hole in the pipe to relieve any form of air pressure.

You should drill this hole directly above the connection fitting at the pump base.

The principles of fluid dynamics are such that a liquid may act as a solid in a static position.
In this static position the fluid may be more prone to act as a solid if there should be added pressure.
Said pressure is exerted by the fluid column that is trapped between the pump outlet and weir of the drainage outlet.
In a case where the pump base sits in a 36" deep pit and exits to a pipe at 7 feet above floor the water column may be 10 feet. If you took that 10 feet and filled a bucket with it you may have 3 gallons of waterX 8 = 24 ponds of fluid pressure applied, calculate the check flap resistance into the equation and you may fluid lock a pump.

Thus by relieving the water column at the base of the pump you allow the pump to discharge unloaded and allow the velocity of this water discharge to lift the check and properly function.

Over the course of a pumps life this elimination of load may earn the pump a 5% capacity towards life and 5% power savings as most pumps elevate their power usage per the respected load applied.
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Old 05-26-2011, 06:39 PM   #10
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Default Re: sump pump relief hole

Frank the plumber is technically correct, but if the condition he describes is occurring, then the simple fact is that your pump is not correctly sized. Every centrifugal pump has a performance curve that describes how much pressure it can overcome at various flow rates. If the pump needs a relief hole to start moving water - it is simply the wrong pump.
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Old 05-26-2011, 07:02 PM   #11
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Default Re: sump pump relief hole

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Originally Posted by nmanitou View Post
Frank the plumber is technically correct, but if the condition he describes is occurring, then the simple factz is that your pump is not correctly sized. Every centrifugal pump has a performance curve that describes how much pressure it can overcome at various flow rates. If the pump needs a relief hole to start moving water - it is simply the wrong pump.

I respectfully disagree. EVERY Zoeller pump I have installed recommends a relief hole. It does not "need" it, but with 3+ gallons of water to overcome when the pump starts, it certainly has proven to extend pump life.


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Old 05-26-2011, 07:18 PM   #12
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Default Re: sump pump relief hole

Quote:
Originally Posted by nmanitou View Post
Frank the plumber is technically correct, but if the condition he describes is occurring, then the simple fact is that your pump is not correctly sized. Every centrifugal pump has a performance curve that describes how much pressure it can overcome at various flow rates. If the pump needs a relief hole to start moving water - it is simply the wrong pump.
Every sump pump manufacturer specifically describes in their installation instructions that you are to use a relief hole when setting up the sump pump and or ejector pump.

While per your theory you may feel that you are correct you must also realize the limits within which a sup pump operates.

This performance curve you speak of is limited by available amps.
The average sump pump operates within a range of 7 to 14 amps.

If you were to size a sump pump per this recommended performance curve you would quickly have a pump that could not function correctly within the limits.
Therefore, given the fact that it is required and in most cases must be provided to ensure that the pump does not lock, it is done.

I have literally drilled hundreds of holes in piping to prevent lock on installations by people professional and non who have argued the drilling of the hole, the where and the why. I have been to court to present a statement as evidence as required in a case where a plumber did not drill the hole and was sued for a fortune in damages.
I took the stand and upon being asked a question presented the manufacturers installation guide to the judge.
I never had to say a word. The hole was even illustrated.And exact location shown.
Go read your guide.
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Old 05-26-2011, 07:22 PM   #13
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Default Re: sump pump relief hole

Quote:
Originally Posted by Holedgr View Post
I respectfully disagree. EVERY Zoeller pump I have installed recommends a relief hole. It does not "need" it, but with 3+ gallons of water to overcome when the pump starts, it certainly has proven to extend pump life.


-T
Yup, The Zoeller has the illustration, I install about 120 Zoellers per year. About another 150 Hydromatics and another 50 or so Liberties. I get about 20 calls a year from people who think they need a new pump and Handy has not drilled the hole, I drill the hole for them and Handy gets displaced.
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Last edited by Frank The Plumber; 05-26-2011 at 08:19 PM.
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Old 05-26-2011, 09:14 PM   #14
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Default Re: sump pump relief hole

The hole being discussed is typically called a weep hole. It is drilled in the discharge pipe below the checkvalve. It's purpose is to provide a path to expel air that can get trapped in the pump housing and prevent the pump from priming and removing water from the pit. It is very good insurance to drill this hole any time you install a pump with a check valve whether or not you think the pump's impeller may lose it's prime. Floats can be adjusted perfectly but what about the sump pump that sits in a basement waiting to remove ground water that has not seen rain for months. Most likely the pit is dry and the air lock condition will occur on the next pump cycle. The problem is air lock, you need to remove the air from the pump and piping.
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Old 05-26-2011, 09:45 PM   #15
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Default Re: sump pump relief hole

Quote:
Originally Posted by KCarGuy View Post
That makes no sense...then why even have a Check Valve if you bleed it off all the way to the waterline?
Check valve stops back flow from going into the pit.

Glad I started this thread, totally agree with the fluid dynamics post. Drilled my hole & mine is working fine, except the float needs adjusting. Coming on too much. My instructions are crap. Does not say a thing about adjusting. We got 3.5" of rain Wednesday, 1.25" today. That's are normal for May in 2 days. Supposed to let up and quit all together by Saturday, so I'll try to adjust the float this weekend. Basement is drying out, nothing got too wet except the floor

Last edited by roofster; 05-26-2011 at 09:47 PM.
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Old 05-26-2011, 10:03 PM   #16
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Default Re: sump pump relief hole

[QUOTE=
This performance curve you speak of is limited by available amps.
The average sump pump operates within a range of 7 to 14 amps.[/QUOTE]

Exactly my point. These are small pumps limited by amp draw for a fractional horsepower 120V circuit. So, they have very low "shut off" head. Which means they can't overcome the static pressure of the discharge system - even at very low flows.

I design pumps for a living and understand the hydraulic properties of pumps. I'm not saying using a weep hole is wrong, just that it is a cheap way of getting a pump to work in a system it is really too small to perform in.
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Old 05-27-2011, 07:06 AM   #17
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Default Re: sump pump relief hole

Sorry you're wrong the weep hole is there to evacuate air. It is not to get a pump to work in a system that it is to small for. The pump performance will not change with or without a weep hole. It will either work in the system or not; the weep hole prevents air lock. You have to size any pump correctly or it won't work. The pump has to overcome static head and friction head during pumping.
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Old 05-27-2011, 10:14 AM   #18
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Default Re: sump pump relief hole

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Originally Posted by 68C10 View Post
Sorry you're wrong the weep hole is there to evacuate air. It is not to get a pump to work in a system that it is to small for. The pump performance will not change with or without a weep hole. It will either work in the system or not; the weep hole prevents air lock. You have to size any pump correctly or it won't work. The pump has to overcome static head and friction head during pumping.
+1

I agree with 68C10. The weep hole is for evacuating air and facilitating priming. Sump pumps are single rotor radial flow centrifugal pumps. They are not positive displacement and do not care if they have to start against the maximum design head. They are not limited by the "7 to 14 amp current draw", but rather by the pump curve of radial flow centrifugal pumps.

The power that they draw is the LEAST when they are "deadheaded" (the point at which flow drops to zero because there is too much head pressure to overcome"). Look at this reference from Gould pumps for a discussion:
http://www.gouldspumps.com/cpf_0009.html
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Old 05-27-2011, 11:11 AM   #19
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Default Re: sump pump relief hole

Quote:
Originally Posted by 68C10 View Post
Sorry you're wrong the weep hole is there to evacuate air. It is not to get a pump to work in a system that it is to small for. The pump performance will not change with or without a weep hole. It will either work in the system or not; the weep hole prevents air lock. You have to size any pump correctly or it won't work. The pump has to overcome static head and friction head during pumping.
See my post #8. I don't think we disagree.
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Old 05-27-2011, 12:02 PM   #20
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Default Re: sump pump relief hole

The market at this point will bear a pump cost og between $100 to $150 on a new sump pump. Ideally you may be correct about the pumps ability to over come the pressure, a larger force applied by a pump would do this. You cannot design your customer. Nor can you design your pumps operating environment.
In many a situation I will encounter multiple pumps on a 20 amp circuit.
An ejector 12 to 15 amps
a sump pump at 7 to 12
a battery back up system maybe another 5 to 7
often an alarm. another amp.
You tell the homeowner that they need another circuit and they argue even against all of the math, sorry but math rarely lies.
All they know is that this works now and I'm not calling an electrician.
So there you have the dilemma.
Now there are certainly more efficient pumps out there than the standard oil cannister junks we have been using, I often use a Glentronics unit in a battery draw situation such as from a sumppro unit to extend battery life, It is how ever a fine line design situation and you can't really get much more out of the situation, mostly due to lack of cooperation and system concept by the average home owner.
And so we have pumps which need holes in them.
And if you observe the system in action, you will see. That the system actually introduces air into the space between the check valve and pump base, this air space is not discharged into the water of the pit, it is forced through the check assembly with the remaining water as the pump operates. Thus the hole is there to lessen head and give the pump a chance to get a flowing stream of water hitting that check valve and punching open the remaining head pressure at the check valve.
Works much the same as this. You have a car with a shitty little engine, at 600 rpm if you gun it it's a total dog, but if you drop the clutch at 1800 you get a little taste of pep, or so you think. Think of it as a cheap stall converter for a cheap pump.
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