Cavitation due to Check Valve Location?

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PrescottGirl

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Thank God for this forum. I've been without water now for nearly 9 days...Help! I moved into this home last March. The home doesn't have a well but instead relies upon water truck deliveries to a 2,500 above ground storage tank. Thanks to this forum, I have learned that I have a sub-par/junkie Flotec FP4012-10 jet pump that sits atop a Flotec FP7120 pre-charged pressure tank, both are rather new. The pump and pressure tank are located in an insulated storage shed. The 2,500 tank is located about 7-8' from the shed and sits slightly higher than the shed on a small hill.

Last week, after a very cold 8 degree night I noticed a small crack in the PVC pipe on the discharge side of the pump. I drained the system and cut out the cracked pipe and completed the repair. I also installed a brass priming tee in the discharge outlet as there was none! Since that time (9 days) I have tried countless times to get the pump re-primed. I've tried every troubleshooting tip I could find on this forum and I'm still without water.

Finally, I came across a post that mentioned cavitation and I think that is what I am dealing with. A check valve was installed on the suction line about 2" from the pump inlet. Symptoms I've experienced:
* When the pump is running, the outside of the pump (not the motor) feels warm- not what I would expect when I am priming with ice cold water.
* When the pump is running I hear glugging and slight boiling sound in the pump case.
* When I remove the top screw from the priming tee when the pump is running a large hiss of air is released followed by a gush of WARM water.
* When the pump is running, there are continuous bubbles around the hand tightened top screw on the priming tee. The brass tee itself also feels slightly warm.
*When the pump is turned off following another failed priming attempt, I hear more hissing and glugging sounds.
* Since moving in last March, the only water "problem" I've experienced are pressure surges which are very noticeable during a shower.

I've attached the best photos of the pump and piping with the check valve that I could get in a dark shed with just a flash light.
IMG_20160217_041613.jpg

IMG_20160217_041846.jpg
Am I on the right track that the check valve is causing the issue? How in the world did they initially get this pump primed with no priming tee in the discharge and the check valve 2" from the pump inlet? If the check valve needs to come out, where do you recommend I cut the suction pipe- before or after the 90 degree elbow (I understand the less fittings the better)?

Thank you all in advance for your guidance. I can't wait to shower in my own home rather than the gym.
 

Valveman

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Yeah it is a cheap pump and tank, but it should still work. You just can't prime the suction line with that check valve where it is. You are only priming the line from pump to check valve, and you can't get the air out of the suction line. You need to move that check valve a lot closer to the storage tank. The check valve needs to be in the low part of the suction pipe, before it turns up to the pump. That way water from the storage tank can flow down to the check valve, and you can prime it the other way from the pump to the check valve.
 

hj

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Why is the valve on the suction line turned off? There is actually NEVER a time when turning it off would be necessary. The check valve should be between the pump and the tank, as should the valve.
 

PrescottGirl

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Valveman- thank you so much. I'm glad this 9 day nightmare is almost over. Off to the hardware store after work to grab what I need.

HJ, I've been turning off the suction line valve after each failed attempt at priming. I didn't know if leaving it open would be a problem. Now I know. Thank you.

Have I mentioned yet how grateful I am to have found this forum?
 

PrescottGirl

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I'm sorry, I have a dumb question. When I cut the lower suction line below the ball valve, is that part of the pipe pressurized? If so, I assume there is another valve by the large storage tank that needs to be turned off?
 

Valveman

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Since your storage tank is 7-8' above the pump, you can put the check valve right after the pump as HJ said. That way you can leave the shut off valve on the suction line where it is, and the 7-8' of water from the storage tank won't drain out while you are making the changes. Just make sure you never close that valve on the suction side during normal operations.

When the pump is not below the storage tank I like to put the check valve on the suction line so the pressure tank can make sure the pump stays primed. But with positive pressure from the 7-8' higher storage tank the pump will stay primed and you can put the check on the discharge side of the pump.

Edit;
Note that is a 1.25" check valve and the discharge on the pump is 1". I would just get a new 1" check valve to put on the discharge side. Preferably a brass or Stainless one as they are better than plastic.
 

Texas Wellman

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Why is the valve on the suction line turned off? There is actually NEVER a time when turning it off would be necessary. The check valve should be between the pump and the tank, as should the valve.

Actually, since the OP mentioned that the storage tank is higher in elevation than the pump, you would need this valve if you need to service the pump.

I have mixed feelings about the check valve location. But, if it HAD been working, I don't see what it wouldn't still work.

This is what I would check: Is the cistern full of water? Is the suction valve open? Is the check valve operational? If the check is stuck closed it would be just like a valve that was closed.
 

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After thinking about what TW said, that check valve must be stuck. That is one reason I don't like plastic check valves. If that check is not stuck closed, you should be able to just open the inlet ball valve, let air/water out the top or discharge of the pump, and the 7-8' of head from the storage tank should prime the pump for you. If it had been working like this previously, then the check valve must be stuck closed.
 

Texas Wellman

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Yeah, the thing that made me think of the check valve being stuck is the fact that the pump shouldn't NEED priming if the tank is higher and has water in it. It should be flooded suction. Also just FYI if the OP is still around the valve is OFF when the handle is perpendicular to the pipe and ON when it's parallel to the pipe. I think they may have the valve shut and think that it's open.
 

PrescottGirl

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Texas Wellman- The cistern is full as I just got my regular water delivery on Monday( the delivery truck was there as I left for work). Last night after work, I removed the check valve from the inlet and repiped with a straight run of pipe to the pump. I had a friend do the actual PVC plumbing so my inexperience didn't result in leaking joints. I opened the ball valve (parallel to the pipe), filled the inlet pipe and pump to the top of the priming tee. We left the priming plug hand tight to allow air to escape and after maybe 2-4 mins opened the hose spigot about 1 foot from the pump. We did get a fairly strong stream of water and air mixture from the hose, but only get a dribble to the closest bathroom faucet inside the house. The pump just wouldn't shut off, so after about about 8-10 mins we turned it off and tried the process again.

So frustrating. Am I likely dealing with a pump gone bad?
 

PrescottGirl

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I just went back out to the pump storage shed to be sure- but when the inlet ball valve is opened on the inlet, there does not seem to be a rush of head water from the large storage tank. In the morning I can post a pic of the location of the storage tank in relation to the pump storage shed to be sure I'm not misleading you on the elevation difference. Thank you to all for your ongoing help. It's beyond appreciated.
 

Ballvalve

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* When the pump is running, the outside of the pump (not the motor) feels warm- not what I would expect when I am priming with ice cold water.
* When the pump is running I hear glugging and slight boiling sound in the pump case.
* When I remove the top screw from the priming tee when the pump is running a large hiss of air is released followed by a gush of WARM water.
* When the pump is running, there are continuous bubbles around the hand tightened top screw on the priming tee. The brass tee itself also feels slightly warm.


No mystery here, she has her answer. Running without inlet water, or a small suction side 'leak' [see last paragraph] With the pump off or on, she would have had water coming out of the plug in the tee if open.

Possibly ran the pump with the valve closed and boiled the impeller. If the pump is 7' or 1' below the tank, sure don't need a 'priming' plug. I would put a 1/4" valve in that priming plug for opening and proving incoming water and air release. Also the pump may have run with an empty tank and cooked the impeller. And it seems to me that the pump may have a check valve built in as so many of the plastic ones do.
I would be sure to have a pressure switch with a low pressure shut off in such a situation. And put some unions in that assembly for changing that pump without a saw for the next time.

I have a 12 stage booster pump set up just like hers with a tank 25'+ above the pump. Still the damn thing has a hard time starting to make pressure - had to add that valve on the outlet tee, and I get air and spurts of water for some time before I can get it to make pressure. Finally, I went on a suction side leak hunt and tightened everything up - now it seems to be reliable. It is amazing that you can have @10 psi of inlet water pressure and not have a drip, but when the pump starts up, it can suck air IN through that joint.

On edit: I am reminded that years ago the pump ran and did not make pressure for about 1/2 hour - but its an iron unit, and so it just managed to melt the Schedule 80 threaded pvc nipples on the outlet. This is not true cavitation, rather just a blender running too long.
 

Valveman

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I just went back out to the pump storage shed to be sure- but when the inlet ball valve is opened on the inlet, there does not seem to be a rush of head water from the large storage tank. In the morning I can post a pic of the location of the storage tank in relation to the pump storage shed to be sure I'm not misleading you on the elevation difference. Thank you to all for your ongoing help. It's beyond appreciated.

The storage tank being 7-8' in elevation is not going to cause a "rush" of water, it is only about 2-3 PSI. But it should still be enough to push the air out the priming plug or a little ball valve, as Ball Valve suggested, which is a good idea.

The impeller could be melted. Or there could just be some debris in the little venture nozzle or jet. Take a piece of wire and clean the nozzle from the cleaning plug.
 

Valveman

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It is amazing that you can have @10 psi of inlet water pressure and not have a drip, but when the pump starts up, it can suck air IN through that joint.

Yeah air molecules are so much smaller than water molecules that water will not drip from a small leak even at 50 PSI or so, while air can easily be drawn in when the pump is sucking.

It could also be a suction leak, but suction leaks are not usually as much of a problem when you have a flooded suction as they are when you are doing suction lift. But if the pump got hot, any plastic screwed into the suction side of the pump has probably developed a suction leak.
 

PrescottGirl

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The impeller could be melted. Or there could just be some debris in the little venture nozzle or jet. Take a piece of wire and clean the nozzle from the cleaning plug.

Thank you everyone. I'll pull the cleaning plug and clean the nozzle. If that fails to help, If I understand everyone correctly, it's likely time for a new pump after locating any potential suction leaks? From all I have read, it seems this pump wouldn't be worth the cost & time of a $50 rebuild kit.
 

PrescottGirl

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I think we have some progress made. I did as Valveman suggested and cleaned the nozzle via the plug below the suction inlet and the pump was able to prime. It's not building enough pressure to shut off, and there was still a faint sucking sound in the pump case as well as air still to be bled out of the priming tee. When I shut the pump off it sounds like water was running back down the suction pipe but was still able to get water gushing out of the top of the priming tee when I attempted to move it. I take it that points to a suction line leak? I tried the shaving cream over the joints to see if I could spot any dimpling but I didn't see anything obvious. Would it help if I got a pressure gauge so I could tell you how much pressure is being built?
 
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PrescottGirl

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I went ahead and pulled out the pump last night to inspect the impeller. With my untrained eye I don't see any damage, but there are a few spots on the venturi that appear to be nicks perhaps? Do these pics help to likely rule out the pump being the issue? I read that PVC ball valves are a common cause of air leaks on pool pumps so am I at the point that I should just go ahead and cut out the pipe below the ball valve in the suction line and just replumb the line up the pump?
IMG_20160222_051634.jpg IMG_20160222_010137.jpg IMG_20160222_010107.jpg IMG_20160222_051906.jpg IMG_20160222_051858.jpg ?
 

Reach4

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Looking for a suction leak, you can have somebody monitor the PSI while you make every fitting joint, in turn, very wet with water. If you hit a joint that is sucking air, the water should slow that air, and the pressure should rise.
 

Valveman

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The impeller looks OK. You could also have a restriction in the suction line. If the pump cannot get as much water as it is trying to produce it will actually draw air right out of the water.
 

PrescottGirl

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Reach4- Okay, I'll pick up a pressure guage tonight and have a neighbor come help.
Valveman- Could that ball valve be a possible source of a restriction?
 
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