March pump keeps sputtering...

This is getting pretty frustrating. I have a March 809 pump. Generally was working great for about the last 6 months. I recently hard plumbed my system. Last time I brewed I had some serious problems with inconsistent flow and "sputtering." Flow would start, then choke off, sometimes, stop, then start up again. I chocked it up to a stuck sparge during RIMS. I had to brush grain off my braid to get flow going. But now I'm just testing my system with water and I'm getting that sputtering flow again. Fast one second, choking off the next with air bubbles in the line.

I have a bleeder valve and an autovent, so I don't think priming is the issue. I've been messing around trying to improve it and nothing seems to be working.


Any ideas? Is it my pump? My setup? Here's a pic. I don't know what to try here so any ideas are appreciated.

I removed the pump head (just the part with the inlet and outlet. Didn't see any problems but the inlet and outlet tubes are hard plumbed, so I can't look inside them easily.

Should I look into the impeller?

I removed the dip tube from the keg and raised it about 2 feet to get more head pressure. Better, but same problem. Must be the pump. Keg valve drains well.

Why do you have an autovent on the input side of the pump? It seems to me that you could be sucking in air through it. Temporarily put a plug there and see what happens.

Thanks for the idea. I'm going to try plugging it tonight as I just added the autovent on the intake thinking it would help my flow issues. Of course, I had to change the plumbing to add it, so now I'm not sure what to look to.

My understanding is that the autovent on the intake will help vent the air trapped in my dip tube. Beerthirty had one on both the inlet and the output side of his pump.

I believe the autovent only lets air out, never in. But I'll try plugging it and report back.

He has an autovent on the input side because thats where it should be. The autovent removes air from the input side so the pump can prime. I think air is getting into his pump somehow from the output side or the input is cavitating. He doesn't seem to have a priming problem as it primes but not not stay primed. I would think if the problem was on the input he would not be able to prime the pump at all. The other thing I don't like is braid. IMHO he would do much better with a false bottom as I would think it would be better at preventing cavitaion..

Sawdustguy said:

He has an autovent on the input side because thats where it should be. The autovent removes air from the input side so the pump can prime. I think air is getting into his pump somehow from the output side or the input is cavitating. He doesn't seem to have a priming problem as it primes but not not stay primed. I would think if the problem was on the input he would not be able to prime the pump at all. The other thing I don't like is braid. IMHO he would do much better with a false bottom as I would think it would be better at preventing cavitaion..

Click to expand...

Sawdustguy, I have to disagree with you. An autovent on the input side of the pump will suck air if there is any restriction in the input line greater than the restriction on the output side. Look at the Watts data sheet, as it specifies that the vent remains closed as long as system pressure is maintained. This doesn't happen if there is any restriction in the pump input.

See this: http://media.wattswater.com/ES-DuoVent.pdf

ChuckO said:

Sawdustguy, I have to disagree with you. An autovent on the input side of the pump will suck air if there is any restriction in the input line greater than the restriction on the output side. Look at the Watts data sheet, as it specifies that the vent remains closed as long as system pressure is maintained. This doesn't happen if there is any restriction in the pump input.

See this: http://media.wattswater.com/ES-DuoVent.pdf

Click to expand...

Your right, I don't know what I was thinking. I had to run into the garage and look at my rig and yup, it's on the output.

Sorry, slightly off topic.

Guy how do you like the Autovent? Seem to work well on your system?

So far so good Ron, I have not had a priming problem since I installed it.

I'm going to start by replacing my quick connects with 1/2" cam locks. The mcmaster ones are actually only 1/4", which I learned by disassembling one. I think that's part of the problem, especially with an autovent. As someone pointed out, seems logical that if there's restriction on the input side, seems like the autovent could be admitting air, a problem I had before I installed the input side autovent.

I'll report back. Also, I want to link to beerthirty's thread where he discusses having a vent on both input and output sides. Gotta find the thread, though.

I just realized that my autovents were broken. The tab at the bottom of each that functions as the vacuum breaker fell out upon removal.

I'll try again with a new one.