March Pump losing prime

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shoebag22

shoebag22

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I just started three tier fly sparging and attempted to pump my sparge water from my keggle to my coleman cooler that was about 6 feet above the level of my pump. I could get a great prime, but I would lose it after about 20 seconds. I ended up having to move the cooler down to floor level to retain the prime... I'm at a total loss as I had zero problems getting an initial prime, but constantly losing it was really disappointing.
 
I am using QDs from mcmaster and all fittings are wrapped with teflon tape, but I will double check... should this pump be able to pump into a vessel 6 feet above?
 
yup 6 ft is doable albite slowly as it just about it's max head height



edit: if you have a pump why going so high? a pump enables you to cut a tier out of your system. my pump is on the floor with my hlt and kettle at 6 inches and the mt at 28 inches.
 
so you use your pump to pull the wort from the mlt to the boil kettle? you basically match the speed of the sparge to the speed of the pump?
 
That's what I do. I have a three tier and use the pump to vorlouf and after vorloufing I pump from the lauter to the kettle. I have an valve on the outlet of the pump to control the speed.
 
HLT on top so it can gravity, MLT in the middle, Kettle on bottom. I just pump, cause I'm too lazy to disconnect the hose after vorloufing.
 
sorry p ump to fly sparge, i find it easier to match outflow speed to inflow this way. plus with my hlt at waist high it's easy to add in water
 
eriktlupus said:
sorry p ump to fly sparge, i find it easier to match outflow speed to inflow this way. plus with my hlt at waist high it's easy to add in water
Click to expand...


so your kettle, pump and HLT are on the ground... MLT is on tier and that gravity drains in to the kettle?
 
I have found that using the McMaster QDs, you will get some air entering on the input side, with the Marsh pump.

Two things you can do, let the water flow from the HLT through the pump, with the pump turned off until the air pockets are gone. This means you do not have the outlet side connected to the MLT.

The other is to backflush the pump with water from the outlet side to the HLT so there are no air pockets. Either of these methods should ensure that you will keep the pump primed.

I do fly sparge with two pumps and have valves to control the flow on the inlet of the MLT and the inlet of the kettle. I do back flush to get the vorlauf flowing smoothly. When I switch connections into the kettle, I have no trouble. I do back flush to start the sparge water from HLT to MLT. This is on a single tier.
 
shoebag22 said:
so your kettle, pump and HLT are on the ground... MLT is on tier and that gravity drains in to the kettle?
Click to expand...
bingo!
shoebag22 said:
I'm using the hi temp silicone. I was seeing large air bubbles/pockets moving from the kettle to the pump...
Click to expand...
this means your pulling air in thru the fitting threads at this point. try tightening the fitting a bit or re-wrapping with tape.
 
Wayne1 said:
I have found that using the McMaster QDs, you will get some air entering on the input side, with the Marsh pump.

Two things you can do, let the water flow from the HLT through the pump, with the pump turned off until the air pockets are gone. This means you do not have the outlet side connected to the MLT.

QUOTE]

This is exactly how I was initiating prime. I actually followed Bobby's video and it worked great... just sucked losing prime after 20 seconds of solid flow.
Click to expand...
 
I don't get any air coming through the QDs at all. I thought that might be true and I've tested it by fulling blocking the siphon tube and the pump will nearly collapse my silicone tubing and NOT pull air through the QD.

I think any air you see in the line is coming from air that was trapped inside the siphon tube and/or ball valve assembly.

Do this

 
Last edited by a moderator:
IMO and best guess, the problem is not caused by an air leak, but it might be due to cavitation. I would suggest positioning the kettle at least 18" above the pump inlet. This will create positive suction head for the pump and may eliminate the problem. The higher the water temp the more prone the pump will be to cavitation and the more positive suction head you have the less chance of cavitation problems. I've learned that it's very difficult to pump water much above 200 F and cavitation can occur at temperatures well below boiling under some conditions. Fortunately, pumping at very high temperatures isn't usually necessary when brewing.
 
Bobby_M said:
I don't get any air coming through the QDs at all. I thought that might be true and I've tested it by fulling blocking the siphon tube and the pump will nearly collapse my silicone tubing and NOT pull air through the QD.

I think any air you see in the line is coming from air that was trapped inside the siphon tube and/or ball valve assembly.

Do this

http://www.youtube.com/watch?v=KUyifHMy9Fs
Click to expand...



this is exactly how I was priming and it would work great at first.
 
Catt22 said:
IMO and best guess, the problem is not caused by an air leak, but it might be due to cavitation. I would suggest positioning the kettle at least 18" above the pump inlet. This will create positive suction head for the pump and may eliminate the problem. The higher the water temp the more prone the pump will be to cavitation and the more positive suction head you have the less chance of cavitation problems. I've learned that it's very difficult to pump water much above 200 F and cavitation can occur at temperatures well below boiling under some conditions. Fortunately, pumping at very high temperatures isn't usually necessary when brewing.
Click to expand...

keep in mind that if I were to place the HLT at the same level as the pump it worked like a champ... it just had an extremely difficult time pumping vertically.
 
I'll get cavitation when pumping out of my BK with the flame on while boiling. However, once I turn the flame off, it stops completely even with the temp still at 212F.

If you fill your vessel with the drain closed (of course), the siphon tube and valve never fill up because of trapped air.
 
Catt22 said:
IMO and best guess, the problem is not caused by an air leak, but it might be due to cavitation. I would suggest positioning the kettle at least 18" above the pump inlet. This will create positive suction head for the pump and may eliminate the problem. The higher the water temp the more prone the pump will be to cavitation and the more positive suction head you have the less chance of cavitation problems. I've learned that it's very difficult to pump water much above 200 F and cavitation can occur at temperatures well below boiling under some conditions. Fortunately, pumping at very high temperatures isn't usually necessary when brewing.
Click to expand...
+1. At high temps any little thing can cause cavitation. Look to have the flow as smooth as possible and try to keep the cross-section of the tubing/valves/etc. as constant as possible. If the cross-section of the flow path goes from large to small and then to large again (sort of like a venturi does) then it can often cause cavitation.
 
SpanishCastleAle said:
+1. At high temps any little thing can cause cavitation. Look to have the flow as smooth as possible and try to keep the cross-section of the tubing/valves/etc. as constant as possible. If the cross-section of the flow path goes from large to small and then to large again (sort of like a venturi does) then it can often cause cavitation.
Click to expand...

pumping 180 degree water through 1/2 inch fittings and hoses... doesn't seem like this should be pushing the limits of this pump...
This probably is all moot since I will be reconfiguring my setup and will not have to pump as high. I must be sucking air in at some point...
 
shoebag22 said:
pumping 180 degree water through 1/2 inch fittings and hoses... doesn't seem like this should be pushing the limits of this pump...
This probably is all moot since I will be reconfiguring my setup and will not have to pump as high. I must be sucking air in at some point...
Click to expand...
But if it's cavitating it's often not really the 'pump' but rather the volatile liquid and the restriction in the tubing/piping. When the liquid is hot it offgases a lot easier than when it's cool (more volatile). If the tubing/piping isn't right then the suction of the pump will pull gas out of solution and create bubbles and the pump cavitates. I see it all the time at work where we pump extremely volatile solvents through hot tubing that's been sitting out in the sun (we insulate it but it still gets pretty warm).

You said that the pump will prime and pump fine but then loses prime. So it appears the pump is up to the task but the cavitation is killing the whole thing.
 
SpanishCastleAle said:
But if it's cavitating it's often not really the 'pump' but rather the volatile liquid and the restriction in the tubing/piping. When the liquid is hot it offgases a lot easier than when it's cool (more volatile). If the tubing/piping isn't right then the suction of the pump will pull gas out of solution and create bubbles and the pump cavitates. I see it all the time at work where we pump extremely volatile solvents through hot tubing that's been sitting out in the sun (we insulate it but it still gets pretty warm).

You said that the pump will prime and pump fine but then loses prime. So it appears the pump is up to the task but the cavitation is killing the whole thing.
Click to expand...

+50,000 You may be able to pump near boiling liquids, as Bobby apparently does, under the right conditions. OTOH, when conditions are right for even a slight amount of cavitation to occur, it will and it will likely interfere with the pump possibly causing it to lose prime.

1. Maintain as much positive suction head as possible
2. Avoid using reducers on the suction side of the pump
3. Use the shortest hose that is practical, especially on the suction side
4. Use the largest hose diameter possible (within reason, of course). This is very important on the suction side.
5. Use hoses (AND FITTINGS) with an inside diameter of no less than the ID of the inlet port on the pump (ie. typically 1/2" for the common March pumps). This includes the kettle DIP tube, etc. Barbed adapters and QD's often have a smaller inside diameter and can cause a restriction.
6. Do not use a flow control valve on the suction side of the pump. It should be used on the output side.
7. Minimize the number of elbows etc, if used, on both the suction side and the output side of the pump.
8. Be sure the pump has sufficient power to supply the desired flow rate at the operational head pressure of your system. Factor in all of the system losses when looking at this.

You can easily test your system using cold water in order to determine if it's a cavitation problem. If it works with cold water, but not with very hot water, you will know right away.

I've learned most of the above the hard way. I no longer have priming or cavitation problems. None and never. I can't help it if I'm lucky.
 
I don't know if this applies to this topic or not, but I have only had one problem (so far) with my pump loosing prime, and I found out my hop bag was stuck in my pick up tube. Once I removed that, the pump primed right away!

I think I am going to apply bobby_m's way ( as I often do ) and use some thin SS wire so that I can get the hop bag out quickly if needed.
 
I had problems yesterday as well. Interesting that my march pump has a 3/4" inlet fitting and yet I am feeding it with a 3/8" sideways diptube. I need to rethink my whole keggle drainage setup.
 

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