March pump problems with hot water

[dirtyal]

I have a march pump 809 HS since one year and lately it is not pumping hot water anymore. My setup did´t change. When I turn the pump on, it pumps for a second and then stops. The sound of the the pumps changes and it stops pumping.
It does pump room temp water normally.
Any ideas?

 

[Cpt_Kirks]

How hot is your hot water?

 

[ThatGuyRyan]

Are you sure its primed? Just a little pocket of air will cut the flow. Also have you checked your hose for any leaks or holes?

 

[GilaMinumBeer]

Sounds like cavitation.

 

[dirtyal]

The water is at 77C, there are no leaks on the system. I was reading just now about priming the pump better. I will do some tests with that.

 

[samc]

It's just a few screws to open the head up and check for something caught inside. I'd also consider that the heat is causing some expansion somewhere and letting air in. Look closely for any cracks in the plastic or your hoses or connections. Might not show up as leaking at this point.

 

[RiverCityBrewer]

Check your thrust washer... I had one completely wear out on my MLT pump. If that guy is not there it can make the pump do some strange things (mainly not work).

 

[dirtyal]

I´ve already opened it and it seems ok, there was nothing caught inside and and no apparent wear.
I will check the priming and try yo use it with the inlet down.

 

[ThatGuyRyan]

How do you prime it now? Do you have the pump located above, below or level with your kettle? Do you have a valve on your kettle that the hose is connected to or do you just drop the hose into the kettle?

 

[dirtyal]

My kettles have 3/4" connections with ball valve and a use a quick disconnect 3/4" to 1/2" where the hose is attached. I use silicone 1/2" hoses on the inlet and outlet. I have the same configuration in all my three pots.
The pump is bellow the kettle.

I´ve attached a picture where you can see my system and the pump. In this photo, it was working perfectly, I am doing fly sparge with two pumps.
Tks.

 

[ThatGuyRyan]

The set up looks good. Before you turn on the pump do you open the valve on your kettle for a few seconds so the liquid flows to the pump. Also is the outlet line at that time empty and the valve going to your second kettle open so the fluid can flow via gravity through the pump inlet to the outlet side. If any liquid is in the 2nd hose going to your 2nd kettle it will not let the pump prime properly and will trap a air bubble in the pump. I myself can’t think of anything else.

 

[dirtyal]

I designed the system so the hot liquor tank would feed the mash tun via gravity and I add the pump to speed up the process.
I open both valves and through gravity the water starts flowing , then I turn on the pump and it gives a burst of water on the outlet and stops.

 

[EarthBound]

How's it going on this?

 

[dirtyal]

I just tried the pump yesterday, with hot water, it will now work and the engine gets stuck, it starts spinning very slowly and sometimes it just stucks.
With room temperature water, it will work perfectly.

 

[passedpawn]

Just buy a new head. I've seen them on ebay for $25.

 

[DeafSmith]

I was testing my new system last week, pumping 160ºF water from a kettle to my MLT and had problems losing prime frequently. It pumps perfectly with either hot or cold water with the burner off - it only failed with hot water in the kettle and the burner on. The kettle has a dip tube in it from the ball valve to the center of the kettle. I found that if I constantly stirred the kettle while pumping that I didn't lose prime even with the burner on. I could always reprime by simply turning off the pump and letting the water flow backwards for a couple of seconds - noticed a lot of bubbles coming out of the diptube almost immediately after turning off the pump, so I think they were in the diptube, the ball valve, or just outside the valve, but not in the pump. I'm speculating that it is cavitation - either sucking up steam bubbles from the bottom of the kettle, or maybe sucking up near boiling hot water right off the bottom of the kettle which turns to steam, maybe due to the Venturi effect as it goes through the narrow opening in the ball valve. I'm going to try another test this week without the dip tube and see if that solves the problem.

EDIT: Tested without the dip tube, only a coupling screwed onto the nipple inside the kettle, and had no problems. Pumped all the water (down to the top of the coupling) out several times and didn't lose prime a single time. Everything else was exactly as in the previous test above with the dip tube.