Wilo pump & expansion tank - need to repressurise

naylorpd · Feb 4, 2020

I live in Azerbaijan where I have a Wilo MC605-EM pump attached to a Wilo LRS 50/10H diaphragm expansion vessel, which pumps water into my house on demand. We have a large water storage tank sitting between the mains and the pump so there is effectively no water pressure, the pump sucks water out of the tank and pushes it into the house.

The meter on the pump outlet by the braided hose is reading 3.5 bar which I guess is just the pressure in the pipework until someone opens a tap.

The pump is misbehaving, going in short bursts of brrr-clunk-silence-brrr-clunk-silence and the water comes out of the taps in the house in bursts. As I understand it, I need to re-pressurise the expansion tank, but I can't find any good instructions on how to do that. I believe that if I don't do it soon it may damage the expansion vessel which I think has a butyl rubber diaphragm.

There's a label on the tank that just says "in case of insufficient air pressure please empty all water from the tank and replenish dry air by using a compressor". I do have an air compressor available.

The pump is connected by threaded fittings on the top and left of the picture. I can undo these easily enough, and that will drain the pump - but I think not the expansion tank as that sits underneath connected by a large braided hose. So how do I empty the water from the tank? And when I've done that, what pressure to I put back into the expansion tank?

ShaunCorbs · Feb 4, 2020

may have split so might need replacing there should be a schrader valve in the opposite end to the flexi might be a cap on it when you press the core in do you get water out or air?

to recharge with air

turn off the suply to the pump (electric)

then turn off the supply to the pump (water)

open the cold tap / item down stream of the pump

there should be a data plate on the expansion vessel to give you pressures

to recharge you just need a bike pump and pressure gauge

naylorpd · Feb 5, 2020

The label says:
The proper air pressure must be:

in booster systems p0 = 0.9 x pmin
in heating systems p0 = ps + 0.2bar
in cooling systems p0 = ps

p0 = air pressure (bar)
ps = static water pressure (bar)
pmin = start-up pressure (bar)

And in a separate box that is like the tank characteristics:

Operating pressure pmax = 10 bar
Test pressure ptest = 15 bar
Preset air pressure p0 = 1.5 bar

I'm kinda lost there....is the answer just 1.5 bar?

But unfortunately, water came out of the Schrader valve, so it looks like I have a split in the membrane. Is this repairable, or do I need to replace the whole expansion tank? There's a flange at one end, can you unbolt that and swap out something inside? I'd be happy to have a go at that if I can get the parts. Do the bolts need tightening with a torque wrench?

This isn't the first time that this has happened, I think the second in about 5 years. What causes this, am I doing something wrong? Or more likely, not doing something I should? How often should I check the air pressure? I have another two stand-alone expansion tanks in my hot water system, both larger than this. I don't really understand what they do...but the heating system is something for another thread!

Many thanks...
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naylorpd said:
I'm kinda lost there....is the answer just 1.5 bar?

And if so, what's the significance of the 3.5 bar reading on the dial? Isn't this also the pressure in the expansion tank?

Meantime, have asked Wilo Azerbaijan about spares...
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OK, I bought a new bladder, about £10, and have a much better idea of what's going on, thanks to YouTube

View: https://www.youtube.com/watch?v=2NMdjft_Ces

View: https://www.youtube.com/watch?v=NPZw83Iypzg

So now I understand that I need to put 1.5 bar into the tank after fitting the new bladder.

When pressurising the tank, the house it's connected to is 3 storeys so there's a head of water in the pipework of about 12 metres. So it seems to me that it's better to isolate the upstream pipework and disconnect the pump to pressurise it. That's easy enough.

Many thanks for the tip to look for water in the valve, that helped a lot to understand what was going on.