Pump runs but does not reach operating pressure


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Old 02-11-11, 05:16 PM
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Pump runs but does not reach operating pressure

I collect rain water which I treat and then store in a 550 gallon tank. From the tank there is a 1-1/4-inch 5-foot riser and then a 20-foot straight run to my pump house (houses filters, UV, pump/pressure tank). The pump is a Sears 1/2HP shallow-well pump that has operated flawlessly for four years mounted on a 39 gallon pressure tank at 40psi with a 40/60 in/out switch.

Notwithstanding insulation (R-19), the recent record cold temps, for the first time, caused the insulated tank-to-pump line to freeze and fracture the couplings/elbows/valves, i.e.., the more rigid components (the pump house is heated so no issues there). I replaced all of the cracked components, pressurized the line to r/o hidden fractures/leaks, verified the tank charge/pump prime and restarted the system. It takes the pump less than 30 seconds to run the pressure from 0-40psi. However, at 40psi, the pump continues to run, the needle on the pressure gauge starts wildly jumping (v. its steady climb to 40psi), but the pressure will not rise above 40psi.

My first thought was the impeller/diffuser assembly. I disassembled the pump and did not find any visual irregularities with these components, i.e., no cracks, the impeller "cups" were all in tact, and both seemed to fit the housing normally. I disassembled the venturi/nozzle assembly and both were clean and unobstructed. I verified that the built-in check valve was operating normally by blowing into the housing, which readily opened the valve. I removed very minor amounts of scale from the parts and reassembled the pump. The issue persists.

Since the pump house is heated, I have to concluded that the cold weather did nothing to compromise the pump. In disassembling the pump I was wondering if it would be possible for a small chunk of ice to sucked into the pump and damage components but, again, I saw no visible signs of damage. A second thought was might there be something "going on" with the pressure tank. The tank pressure has always remained at 40psi (before pumping water) but if the bladder leaked would that cause the issue (I removed the shrader valve thinking if there was water in the tank, there might be a bit of a spray as the air bled from the tank). Nothing. And, as I mentioned, I have determined that there are no leaks in the line.

So, regardless of my findings, I would be interested in folks thinking as to why the pump would readily pressurize to 40psi but go no higher. (My next step is to replace the diffuser/impeller but hate to spend the money just to test my theory)

Thanks, Monk
 
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Old 02-11-11, 07:57 PM
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Hi and welcome

From everything you say it does sound as if the pump is bad. There may be no visible signs of ware but the tolerances in the pump may have wore to a point in witch the pump cant build the pressure it needs.
Also from the symptoms, it could be a cracked jet assembly. I would check the jet one more time just too be sure theres nothing in it and its not cracked.
 
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Old 02-12-11, 11:22 AM
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Originally Posted by waterwelldude View Post
Hi and welcome

From everything you say it does sound as if the pump is bad. There may be no visible signs of ware but the tolerances in the pump may have wore to a point in witch the pump cant build the pressure it needs.
Also from the symptoms, it could be a cracked jet assembly. I would check the jet one more time just too be sure theres nothing in it and its not cracked.
Thanks Dude,

I will do as you suggest and post back.

BTW, this AM I ran the pump and, after 5 minutes, it ran the pressure up from 40 to 45psi (gauge needle no longer jumping around; jumping might have been due to initial air in line). I have to conclude that, if we are talking pump issues specifically, the pump issue is one hell of a coincidence, i.e., occurred at the same time the line just happened to freeze but has nothing to do with the freeze/repairs; there is a part of me that just does not want to accept that coincidence.

Regarding bad pump: the motor hums normally so would it be sufficient to replace venturi/nozzle and the impeller/diffuser plate (or just impeller)? My thinking is, there is nothing else in the pump that handles/pumps water.

I'll post back later today after I reinspect the guts.

Monk
 
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Old 02-14-11, 11:03 AM
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First off, while I am very experienced in plumbing installations and operations, I have never had the occasion to TS well pumps so much of my conclusions are intuitive, in part based on what I am able to discern from researching the issue.

I had hoped to attach a JPEG of an exploded view of the pump but do not see that the forum permits such (other than a URL link but could not find an exploded view online). Let me know if I missed an upload link.

I disassembled the pump and was able to verify that none of the components appear to be worn or damaged, i.e., the impeller is absolutely in tact, as is the diffuser plate. The jet is a simple enough plastic 5/8-inch nut with about a 3/8-inch orifice. The venturi is a 4-inch tube with an ID of approx 7/8-inch. No cracks, chips, nothing.

In a word, nothing appears so much as worn, let alone broken. When I reassembled the pump and ran it, within 10 seconds it pumped up to 40 lbs but, with motor continuing to run, the pressure abruptly stopped at 40psi. Then, motor still running running, the pressure suddenly dropped to 20psi. (The attached pressure gauge corresponds to my digital tire gauge at the tank valve so I must assume the pump gauge is OK; I have also verified that the pump check valve creates an absolute seal against back flow). I continued to run the pump and the pressure began to slowly rebuild to 40psi (about 2 minutes) and then continued to rise to 60 psi over the next 5 minutes and then stop normally.

I drew off water to allow the pressure switch to cycle; the pump came on at 40psi and, after 3 minutes shut off at 60 psi. So, now the pump works but rather slowly.

My question now is this: the venturi in the front half of the pump housing (clamshell that forms the water chamber) slides into a port in the diffuser that directs water to the impeller. There is an o-ring at the end of the venturi that creates a seal between the venturi and the port. When I separated the front half of the pump, I noticed that there was very little resistance, i.e., the o-ring is not very tight in the diffuser port.

Perhaps all jet pumps are the same so maybe one can tell from what I have described: if the o-ring, by not creating a very tight seal, allowed pressurized water to blow by it around the venturi and back into the water chamber, I imagine impeding water flow through the impeller, might this be the cause of the very slow pressure buildup? Regardless, the o-ring is an odd size so I had to order one and will post back with results when I replace it.

Thanks, Monk
 
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Old 02-14-11, 03:36 PM
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Oops: read the upload sticky!

Guess it would be best to read the stickies before I post, eh?



Relating this to my previous post:

The venturi (12) has an o-ring (11) at its end. This is inserted into the diffuser plate (8) which feeds water to the impeller (7). So what I am wondering is: if the o-ring does not furnish a tight seal, would the pressurized water blow back by the ring and somehow compromise the water flow to the impeller - thus causing the tank to pressurize more slowly?

Sorry for the by-the-numbers post.

Monk
 
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Old 02-14-11, 05:48 PM
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does the pump in question use a plastic head, or cast iron? if plastic, i'm not surprised at all. they seem to work "ok" until one day something happens and the pump "runs hot" for a while. when this happens, 4/5 times the pump will never be the same again. everything can appear fine, but it wont be "right". might take a long time to build pressure, might not build pressure, might not pump as much volume, etc. this is the main reason i steer clear of plastic pumps, i've spent several hours cussing at different models in the past.

if the pump does in fact have a cast iron head.. then somebody delete this post. lol
 
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Old 02-15-11, 09:37 AM
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@Justwater

I note that my uploaded image did not post; I will try again.

The pump does, indeed, have a plastic head. However, this pump serves a system that averages 5 gallons a day. Given its 39 gallon pressure tank, this 4-year-old pump cycles once every three days. The pump has never overheated, has never taken >30 seconds to pressurize the tank to 60psi, and shows no signs whatever of defects in parts, housing, external seals, no leaks, etc. It now takes about 2 minutes to pressurize (for whatever reason it seems to be taking less and less time) but in that time, the pump gets only slightly warm.

Intuitively, if the components/housing exhibit no visible defects, I cannot immediately grasp what might be the cause of the issue vis--vis the plastic head.

I am awaiting the new o-ring and will post back with the results after I replace it.

BTW, I posted elsewhere a query regarding temporarily increasing the effectiveness of the o-ring while awaiting delivery of a new one. I should think that plumbers have devised a temporary "fix" when a part is not immediately available. I assume the existing o-ring has lost its resiliency (although it appears to be in perfect condition) and no longer furnishes a tight enough seal against the walls of the diffuser port. What I did was to wrap a few turns of teflon tape in the o-ring seat thinking that it would, effectively, increase the diameter of the o-ring thus increasing its pressure against the post walls. Is that was has accounted for the slight improvement in performance, I don't know. Stay tuned.

Monk
 
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Old 02-15-11, 09:55 AM
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when the pipe froze between the pump and tank, did the pump run and "deadhead" against the ice, or excessively cycle for any length of time? if so that's "running hot" as well. I understand the concept is hard to take in and I'm not faulting u for trying to get to the bottom if it, especially if its never ran without moving water. just fyi, cast iron jet pumps rarely have these problems.
 
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Old 02-15-11, 03:49 PM
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@Justwater

Thanks for your continued interest.

First off, I am very conscious of running the pump against a deadhead if only because the install manual urges that caution on every other page in giant letters; I have never ran the pump as such.

In anticipation of radical freeze warnings (we hit -13 degrees, breaking records back to the days of Noah - some 40 degrees below our average lows; you may have heard that in El Paso, 100 miles south of me, municipal water storage tanks burst and neighborhoods were flooded as above and below ground mains burst) I drained my water line at the base of the riser but, unfortunately, I inadvertently installed the 20-foot straight run to the pump with a slight downward slope toward the pump - thus the freeze. The water in my 550 gallon storage tank turned into a 2-ton block of ice. I inspected my 20-foot line and noticed that all of the rigid fixtures such as elbows, check valves, ball valves, and connectors had cracked; the sch40 pipe was OK. Eventually (warmer weather), I was able replace the cracked components, manually fill and pressure-test the line for leaks and then, and only then, did I restart the pump - which, by the way, I had shut off so it would not cycle against the empty line; the pump has a low pressure switch regardless.

So, long story short, when I shut the pump down before the freeze hit it was running normally; after the freeze and subsequent supply line repairs, I restarted the pump and discovered the issue. I have a remote thermometer in my heated pump house and observed that, during the freeze, the temp did not get lower than 40 degrees.

I am at a loss and, although I am not disputing your observations with respect to plastic pump heads, you have to admit this is one hell of a coincidence. Before replacing the pump, I am going to limp along until I get the replacement o-ring; my psyche otherwise rebels against spending $300-plus for a new pump that runs once every three days.

Thanks again,

Monk
 
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Old 02-15-11, 06:56 PM
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ok, now I understand what u meant by the freeze.

I hope the o-ring is the culprit. one thing is for sure, cast or plastic.. the tiniest little pinhole of a suction leak in the run from the tank to the pumps impeller can cause wacky problems. good luck.
 
 

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