Irrigation pump woes...

[MikeeB]

I know this isn"t a proper place to ask this, but I haven"t found a more active farming group.

I"ve used this pump for 9 years, and its become increasingly difficult to get started. I"d replace packing and it would work again, but still, never as easy as it had in the past.

Its a centrifugal irrigation pump (3-phase, 5hs). It just won"t build up pressure and suck water after initially starting it. I"ve replaced the packing, cleaned the intake, checked the intake all the way up into the pumps intake.

When working correctly, I"d prime, shut off the prime valve, start the pump - the pressure jumps to 40-50#.

When its not working so well, it bounces between 5 and 15# before building up pressure. I usually have to crack the outflow valve to get the pressure to climb - before opening it up fully.

Now, I start the pump, it sits at 0# for about 30 seconds, then climbs to 3-5# and sits there until the packing gets hot and I shut it off. No water comes out around the packing.

Strange thing is, nothing really changed since I turned it off last (a week ago). It was hard to start then, but never this bad.

I replaced the parts to my hand prime pump since the rubber had an aged wore out hole in it - but this new one seem different. When I used to use the hand prime, I"d pump until water comes squirting out .. now when I pump, I feel it getting stronger as if its filling with water, then it then suddenly stops me from pumping (as if its full... maybe this is the way the backflow nipple is supposed to work?? -- its been a long time since I"ve had new prime pump components...). Some water does come out of the prime pump, but very little compared to the stream I"d get before. Which is correct?

I"m just spewing info in hopes it helps someone go, "aha! you goof, here"s what you"ve done wrong...!"... maybe??

He"p?

Thanks!

 

[Anonymous-0]

I found gravel in the impellar on a pump one time hah to make a tool to break them up!!

 

[wisbaker]

Packing is supposed to leak!! Back off your packing gland a little and get water through the packing, the water lubricates and seals the back half of the shaft. When you replaced the packing did you take ALL of old packing out? What did the shaft look like in the stuffing box? If worn or rough it might not seal What does the impellor look like? it could have gravel or silt clogging some of the vanes. Is the impellor or suction cover worn? As they wear pump performance drops off until they quit. Some pumps you can adjust the impellor position to cover wear. Has the water level you are pumping FROM changed? Pump performance is a differential from supply level to discharge level (considering flow/pressure). If you add distance on the supply side you loose on the discharge side, and it is not a lineal relation. Hope this helps-SBB

 

[MikeeB]

Yeah, I hear that - but all is turning freely. I did crack the case to check the impeller intake - all is free from stuff (wood, grass, etc), and the unit turns freely.

 

[MikeeB]

Thanks - and right, the packing should leak. I'm just saying I'm not getting a drop out. I've replaced the packing before and have it tightened just enough to where it definitely should be throwing water out. I've adjusted it to different tightness just to see what can be done.

I pulled all the packing out, used my fancy iphone cam to look in there - kept pulling rows of packing until I saw metal. The shaft didn't seem to appear worn. But as you say, over time maybe.

I think I need to pull someone in that knows pumps - maybe I'm doing this packing gig wrong (although I'm doing it as I have for the past 10 years). I never know though as I've never been instructed correctly other than from what I read in the pump manual.

On the hand prime pumps, if you've ever used one - I'm curious how they are supposed to work. Pump and water shoots out the blow hole? OR Pump and it just tightens up (as its doing now)?

My prime pump is connected to the outlet, prior to the outlet valve - between the prime pump is a 1" antibackflow gig (1" nipple with a bearing surrounded by two nylon stops).

I'm just wondering if I'm getting enough water filled into the line between the outlet valve and the inlet at the water of the irrigation ditch.

And nope, there is no change in water level. I even climbed in the ol leech infested ditch and cleaned the intake line. =)

Thanks for the ideas. I really do think its packing or packing housing/shaft related. But the way this prime pump is working (or not working) has me wondering also.

Its going to be 97 today and for the rest of the week.... I gotta get this thing going. Wish there were a pump maint feller around this valley... ugh.

 

[Jerry/MT]

I have a a couple of 10HP Cornell centifugal pumps with Byco primer pumps on them. When I prime them the primer pump will eventually be unable to be moved, that means the main pump inlet is full of water AND the main pump outlet throttle valve is not leaking nor is the packing leaking significantly (I think packings always leak something). The check valve in the primer pump is also closed. I start the pump motor holding the primer pump handle down and slowly crack the throttle valve open to allow the out let flow to start. I have a half mile of maanline to fill (~3500 gallons)and I can"t open up the throttle valve immediately because the low pressure switch on the pump would trip off. Besides, the pump would be running in full cavitation which is not good for the impeller).
I let the main pump run for about 15 minutes until the outlet pressure in the mainline starts to rise.I do not monitor the pump pressure, I monitor the pressure in the manifold that supplies the mainline. I then slowly open up the throttle being the system up to operating pressure.

If your pumps are worn (wear ring clearance too large),their flow capacity will be down but they will make about ~=10 % less indicated pressure than a new pump (I just had mine rebuilt last year and they put out about 5 psi more indicated pressure than before the rebuild but the capacity really increased.
i have had several cases of difficulty priming and they were due to leaky throttle valves. If your system is out side and if you leave your throttle valve closed in the winter, sometimes residual water can freeze and warp the valve plate or the valve guides so that it will not seal. It makes for a difficult prime and sometimes keeps you from starting.

Apparently you have a valve between the primer pump and the inlet pipe that you close once you have the pump primed. I do not. Are you sure that valve is not leaking and allowing the prime water to leak back or air to leak in. Try priming and holding the pressure with just the primer pump and then starting, eliminating the primer valve.

Wear in the pumps also can affect starting performance. Is your water "dirty"( i.e. lot of sand or dirt in the water)? That can cause excessive wear.

hope this helps you.

 

[MikeeB]

Thanks Jerry, sounds like we have the same startup procedure. Which usually works for me. I too have a little more than 1/2 mi of 4" to fill.

The water is dirty and so I do suspect wear. But I'm going to post a follow up to what just happened on the main thread. In short, it started and went to full pressure!! I then cracked open the line and let water flow - I thought I had success... then after about 2-3mins of running, it lost pressure and quit. ARRRRGH

I can see it being worn and hard to start... but to have it start up just like normal and run fine for 2 minutes - then die again? I'm lost.

 

[MikeeB]

Well, I'm even more lost now.

So, after coming in to read your replies -- and escape the heat -- I just went back out to try again. I loosened the packing nuts to finger tight (but no different than I have been doing in several prior attempts). Pumped up to prime - shut the valve - started the pump - PRESSURE! A FULL 50PSI!!

I let it run for a few seconds, then cracked open my outlet valve... as I always do, pressure dropped, as expected, down to about 30psi. I usually drop it to just above 20psi, the threshold for my pressure switch. Its blew water like a banchee down the outlet pipe (I thought I had success!). Then I walked over to my car, feeling cocky... it shut off.

And ever since, latest attempts are back to the same symptoms. The pump starts, but no pressure at start... then it creeps up to about 5psi and stays there. If I open my prime pump valve, about 5psi of water starts to pour out the prime pumps outlet hole. But it never rises from there.

I even let it run for a few minutes at 5psi hoping it would allow some water to leak into the packing and help build a seal.. nothing.

So the question I'm beating my head over:
Why would it start and run with normal 40-50psi pressure one time - where all prior and following attempts only get me 5psi?

I am thinking packing or the packing housing of some sort... I just don't know. Maybe someone could enlighten me to how packing works? Is there something I need to do differently? I'm cleaning and inserting packing per the manual - and as I have for the past 10 years... which could be very wrong as far as I know...

ugh.

 

[Jerry/MT]

Is the bottom of the primer check valve above the top of the pump? It needs to be to fill the pump.

 

[MikeeB]

yes

 

[wisbaker]

Sounds like it is cavitating-pulling in air some where instead of water and air don't pump very well. You may be sucking air in through the packing or a leak on your intake piping check it all.

 

[Anonymous-0]

Sounds like your sucking air, or something plugging up the intake line

 

[John Harmon]

I would suspect a plugged inlet pipe.Are you pumping from a pond,a creek,a river,or? Debis or a dead animal or some thing large enough to plug the pipe? If you are pumping from a well or cistern maybe inlet is packed with dirt or sand.

 

[D7 fever]

must have an air leak on the intake side somewhere.
bad joint, hole in the pipe/hose. a 1/4 inch hole would cause those problems

 

[Jerry/MT]

It sounds like it"s loosing prime.

One other possibility. Does it have a thermal reset on it? That protects the motor from overheating. Is that tripping? I"ve had that happen. Usually there is a button you press on the overheat relay to reset it.

 

[MikeeB]

It does seem like its losing prime - I still have a feeling its something to do with the packing. I'm going to go in and get another couple feet of packing rope and try again tomorrow.

No thermal switch. If it had, that wouldn't allow the pump to even turn on - yah? Regardless, its just a pressure switch.

Thanks for the help with your ideas. Much appreciated. I'll post back after I repack it .. I'm getting good at this pack/repack gig. fun fun.

 

[Kansas Cockshutt]

What is the distance between the pump and the supply ditch? If it is short, then disregard this. If it is a long run, you could have an obstruction in the pipe, you would have enough water to get primed and start pumping, but the obstruction causes the pump to start sucking air/loosing head and cut off. Then it would take a while for water to re-fill the supply pipe enough to get the pump going again. Just a guess for you, can"t see your setup from here. HTH.

 

[Dieselbreath]

I had an irrigation pump that wouldn't put out much pressure. The water company guy kept telling me the pump was shot. Didn't believe him because it worked sometimes. Turned out to be a empty soft drink can in the intake.

 

[gbs]

i bought a 5" hale pump driven with a 6 cyl dodge motor from and elderly neighbor that he used to irrigate out of a pond that he kept full with well water.noticed he had a gate valve and hose adapter installed in the suction pipe an also had a brass check valve on the end of the suction pipe between the pipe and strainer, wandered about all this because what little experience i'd had was with pto pumps fairly simple to prime put suction pipe with no check into water close spring loaded discharge valve open valve on primer pump until it got tight and water can out of the diaphragm shut primer valve start tractor run it part throttle discharge valve would open against the springs when lines filled set throttle for pressure and forget it, no so with this pump could not get it to hold prime it would start to open discharge valve then quit i replaced shaft packing's,opened up the pump nothing wrong,checked discharge valve nothing wrong,also opened up the check valve on the suction pipe nothing wrong, replaced hose between the pump and suction pipe ,finally it primed pumped ok ,next time same trouble just kept trying it would catch worked ok, next try pump primer a dozen strokes caught right up,all it would take was a very small amount of air and it would give trouble, i figured out why he had the valve in the suction line he would hook a water hose to it and push the air out, sounds like you may have an air leak some where

 

[Jerry/MT]

What do you mean if it had a thermal switch it wouldn"t allow the pump to turn on? I don"t understand that comment. It"s not that hot where ever you"re are at!

When I repack mine, I first remove all the old packing. I cut the packing material with a sharp utility knife to a length that completely encloses the shaft with the packing. I insert the packing making sure that the slit is offset ~ 120° with each sucessive layer of packing. i use the packing gland to shove the packing downthe shaft and then retract it and put in another layer.

 

[MikeeB]

Ok, what is the purpose of the thermal switch then?