# Anti vac valves



## matharon (Dec 22, 2014)

Some months ago I replaced the anti vac valve on my Wega Nova (HX machine) as it was leaking when the boiler was coming up to temperature. At the time I was puzzled over the way the valve was supposed to work but as the problem appeared to have gone away after I fitted a new valve I forgot about the matter.

The presence of water occasionally under the machine seemed to come from the drain tray sump which can get an airlock sometimes. However, a lot of water under the machine last week showed that the problem had returned (or never went away...) and I have stripped and cleaned/descaled thoroughly and looked more closely at how it works and remain puzzled.

The valve is the long stem version where the pin sits into a cone when under pressure and then falls to release any vacuum on cooling. The seal does not leak when under pressure but during the heating phase there is an expansion of water that leaks past the pin for quite a while until the pin "pops" up into the seat.

The pins is metal and relatively heavy and there does not seem to be a logical way for the pin to seal without water passing in the heat up process.

I have tried leaving the steam wand open during the heating phase and then shutting it so the pin seats more quickly and this does improve matters but there was still quite a leak.

I have ordered another valve with a bleed tube (http://www.ebay.co.uk/itm/161961740559 ) that will avoid a mess and has presumably been developed for the type of leaks that I am facing.

Is it possible that the cup on the underside of the pin is meant to sit on a spherical float that would reduce the initial seeping and I have a part missing?

As almost all boilers seem to have a vacuum breaker valve and the majority are either a short or long pin standard type I would welcome any suggestions how to prevent the warm up leaking. Do your machines have any seepage during the warm up phase and is some to be expected?

Almost all threads on this and other forums about anti vac problems seem to relate to leaking under pressure and the need to descale or replace periodically but that is not the problem here.

Any thoughts would be appreciated.


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## El carajillo (Mar 16, 2013)

Is the boiler over filling ?


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## matharon (Dec 22, 2014)

Not sure what you mean by overfilling but when switched on there is expansion through valve hole.

when anti vac is blocked (by asbestos finger) and steam wand open there is only very small dripping during expansion.

There is not a constant flow which I think is what you are asking.


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## espressotechno (Apr 11, 2011)

There are several variants of anti-vac valves. They all bubble & hiss to some extent until the steam pressure closes them.

The valves with a small, short shaft close earlier than heavier shafted ones, or ones with a ball.

It may be possible to fit an "eggcup" around your a/v valve, to catch the water droplets until the boiler heat evaporates them away.

On a commercial machine the a/v valve should last around 2+ years before the internal rubber seal hardens & leaks ( a few valves seem to last forever !)


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## matharon (Dec 22, 2014)

It is definitely more than the odd droplet - almost a steady dribble at first maybe about 30-50cc until near boiling when it "pops" into place. seems to be less when steam valve is open which dripps 10 - 20cc


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## matharon (Dec 22, 2014)

I think the drain tube solution (see link to supplier) should be better than egg cup and await the new fitment.

But I remain puzzled about the principle of expanding or bubbling water raising a pin against gravity until there is steam to hold in place.

With a long pin valve is there much "play" between pin and hole in seat?


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## coffeechap (Apr 5, 2012)

it seems like your boiler level probe may not be deep enough into the boiler and is thus over filling which will depreciate the expansion space in the top of the boiler.


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## matharon (Dec 22, 2014)

Aha!

That makes sense I think.

Is there a standard "air space" above the water level?


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## espressotechno (Apr 11, 2011)

The ratio of water to steam in the boiler is usually 2:1 i.e. boiler is usually 2/3 full of water.


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## jpaul__ (Feb 19, 2016)

I am also considering the anti-vac valve with the tubing, description says this has a ball bearing, so seems

like a thrird variety compared to short and long pin version.

when I dismantled my long pin I could not see any wear on the Teflon(Viton) o ring seated on top of pin (I need

to take a picture) could you see any difference with the new part ? seemed daft cannot replace just the

o ring and must get the complete part (where is the anticipated wear)

I only de-scaled the part (no pulycaf) but wondered if I should have even used some kind of metal cleaner to

ensure surface was as good a possible.

I did pull and clean the high and low boiler level 'rods' on mine so think the appropriate air gap is there but it sputters

a bit nonetheless (need and endoscsope to inspect inside boiler)


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## matharon (Dec 22, 2014)

I will have a closer look tomorrow but the impression was that water was almost up to the top and it started to rise out of the hole pretty soon after switch on.

The probe does not look to be adjustable so perhaps the electrics are faulty. Would it be default on or off presumably in series with the pump relay.

No need for electric danger warning.


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## jpaul__ (Feb 19, 2016)

if high water level probe had scale on lower end touching water I assume this could give overfill, but mine bz02 were stainless

(I assume they all are) so little prospect of scale sticking


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## espressotechno (Apr 11, 2011)

Scale does stick to s/steel probes ! Remove, clean & refit. Try to set the probe to stop the inflow when the boiler is 2/3 full.

* Drain off some water & see if the cleaned probe stops the pump at the 2/3 level.

* Check the probe wiring: Earthing the lead against the boiler casing should stop the pump immediately. If so, then the probe is defunct.

Occasionally a probe will just fail - new ones are cheap.

If the water level is almost at the top, then the inlet solenoid valve piston may be faulty, allowing water to slowly leak in.


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## matharon (Dec 22, 2014)

Many thanks for all your advice.

Family duties will prevent working on suggestions until after week end.

Will advise when have found problem/solution.


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## matharon (Dec 22, 2014)

Quick update as promised.

There was scale on the probe (now removed fully) but whether this was enough to prevent it working is doubtful.

I did not go through all the electrics as pump was not overrunning so assume this was OK.

Have fitted the new valve with overflow tube and this works a treat. There is still about a quarter teaspoon bubbling out during heat up until the valve pops closed but as this now routed into tray I have no spillage or risk of shorting.

I accept I may not have got to the full cause but time has prevented a more thorough solution.

That is for next time...

Thanks for all your advice.


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