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pulsing pond
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Posted by vundril 8 a Dallas TX (My Page) on Wed, Jan 20, 10 at 14:09
| I hope somebody can help me with a diagnosis of my pump/plumbing problem. My 3 year old Sequence 750 is pulsing water thru the bio filter and split bypass to the waterfall at maybe 1/3 of capacity before problem started a few days ago. Whole system has worked great until problem was precipitated by electrical shutoff to install new dishwasher and when I restored electricity I later noticed the pump seemed to be working normally but it would pulse water out of leaf basket and cease pumping for several seconds until inflow of water refilled basket. Plumbing is 2 inch pvc buried halfway down below surface depth of pond and then rises underground to pump at ground level behind biofilter. Naturally I have topped off primer pot leaf basket. I note that I can remove basket cover and watch and the water be pumped out and then refill to almost the top of basket in regular 20 second cycle.
The pipe is either partially blocked (I have run garden house most of it's length) or pump is losing it's suction power or system has air bubble or I am at a loss ....any thoughts on this problem? |
Follow-Up Postings:
RE: pulsing pond
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| Why is the leaf basket not full of water all the time? Did you check the impeller for something that is impeding it? |
RE: pulsing pond
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| I do not suggest that you run the pump with the cover off the primer pot for any period of time. What happens when you remove the lid is the pump sucks the water out of the primer pot until it sucks in air. Once the volute on the pump is full of air the water in the pipes going out of the pump leaks back through the volute and into the primer pot. The pump is not designed to pump air. When you pump air the impeller cavitates causing wear on the impeller, seal, and volute. If this cavitation gets bad enough the pump will self destruct. Also this is not telling you what is wrong with the system. Also on this pump the impeller is screwed on the motor shaft with glue holding it in place. This makes this pump not a good pump to run air through the pump. So getting back to your problem. The intake pipe can not be partially blocked unless there is an air leak or trapped air in the suction pipe between the clog and the pump. If the pipe is partially blocked the only thing that would happen is the output from the pump would slow down to the amount of water that could get past the clog. This will cause the pump to suck harder to get more water putting a lot of strain on the seals in the pump. The only problem with this possibility is if the pump sucked in air to cause your pulsing the pump would lose primer unless the pump is flood suction. So the next thing is to ask you some questions. Is the intake to the primer pot above or below the water level in the pond? When the pump is running and looking through the cover on the primer pot you are going to see the water level in the pot go down and then a flush of water flow in. The question is does this water flowing shoot across the basket and hit the opposite wall or does it flow in gently? If it flows in fast does the pot empty out quickly or does it slowly go down? The last question for now what kind of fitting and valves are there on the suction piping and where does the pump suck from in the pond? Mike |
RE: pulsing pond
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thanks for the responses. Yes, I removed cover and checked impeller. It turns freely and pump sounds normal.
I removed cover the basket just for a moment to get a good look. The action is a pump of water that empties basket by 2/3 to bottom of pump intake, and then primer pot refills to near top till next pump 'pulse', full action every 20-25 seconds. Mike, the intake to the primer pot is maybe a foot above pond water level. When pump is off, I suppose due siphon action, the basket will refill itself with modest gentle flow. The thing is, with the pump on, pot cover on snug, there is not the usual action of the last few years 24/7, where as you ask, the water would gush in maintaining full pressurized pot. The refill rate is not much better than when pump is running. The pipe intake has screw on pvc filter cap (unclogged) located halfway down on the front side of the pond. The pipe remains buried below pond level until it pops out at the pot using to two 90 degree turns. No valves or other plumbing. In fact I have run the garden hose all the way that point from the pond intake. I gather pump is working fine, but somehow, somewhere there is air in the loop preventing a good suction. Hope that explains things a bit better. P.S Just found by bluegill of five years floating on surface yesterday. He was getting the near the end of his lifespan I guess. But it sure is unhappy coincidence at this time that I haven't been running pump for a couple of days. I have low fish load, many plants and cold weather until last couple of days and not feeding so doubt water quality was cause but... Arrrggghhh??!!! |
RE: pulsing pond
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| Vundril, The first thing that I would check is if there is an oring on the lid to the primer pot and that there is nothing caught in the oring that would prevent the lid from sealing. This is one of the three places that existing system can let air into the pump. The second is the union between the priming pot and pump. If this is a problem then when the pump is off this union would probably drip water. The area is the threads on the male adapter that screws into the primer pot. With age the threads on this adapter may allow the primer pot to suck in air. You are leaking air into the primer pot. The question is will this going to stop your problem. If fixing the air leak doesn't stop the problem it will at least tell us where else to look for the problem. The only reason I don't know if this will fix the problem is the pump is not acting normal. A normal pump when the lid is off the pump and the pump is started the water will pump out and not flow back in at least not in 20 seconds. This tells me that the impeller and volute are worn. It might be worn to the point that the pump can't build enough vacuum to lift the water from the pond level to the primer pot.
Mike |
RE: pulsing pond
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| I have 3 of these pumps. Mike is giving good advise, it sounds like air is getting in. However, the second post is very good too: I'd check the impeller again. These pumps have a closed impeller and stuff can accumulate inside the impeller passages that you can't readily see if you're not looking for it. I take both inlet and outlet pipes off when I chack and clean the impellers annually; easily done since I used Fernco fittings on each side. |
RE: pulsing pond
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| Viola!!! We fixed it! By we I mean you guys and my girlfriend and my blind persistence. I was looking on internet at new pumps and noticed o-ring for sale for leaf pot and thought, whoa, mine has no o-ring on lid at all and hasn't for at least a couple of years or more if it ever did. So I jokingly asked my girlfriend for some lard to temporarily 'seal' the lid to the leaf pot. She suggested saran wrap and so a wrapped lid with several layers and got it on snug, even though it has always seemed it was snug and sealing before, and the flow kicked off as strong and beautiful as I every saw it. Not sure what ever happened to o-ring or how it worked as well as it did until days ago, but thanks for your input. |
RE: pulsing pond
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| My guess is the lid had the oring until the last time you took the lid off. And if you look around you may find it on the ground. Without the oring I doubt that pump would work. A selfprimimg pump will work somewhat without it but not well. There is nothing that holds that oring on the lid so it is easy for it to fall off. If it did work without it the flow would be a lot less and there would be a constant flow of air bubbles. The pump running even a few days like this would wear the pump out. Mike |
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