What is this please?

[MtB]

knocking is air,

 

Not in my experience. Air normally results in tiny ticking noises rather than 'knocking'. When most punters use the work 'knocking', they mean something more serious, often the sort of clunking noise that originates from water boiling in the heat source heat exchanger. So Tiggers, can you expand on the knocking noise? I imagine its pretty loud for it to have driven you to consider ripping it all out!

 

When you you notice it? IS your calorifier heated by a solid fuel stove? Does it do it ALL the time or only occasionally?

 

Any water at all discharging from the PRV suggests the system pressure is rising about 3.0 bar, whcih it Bad News and indicates something is wrong.

 

Mike

[Tiggers]

I think it is trapped air, but it is VERY loud. It is a cross between a knocking and ticking (how unhelpful is that!).

 

I dont have a calorifier, all it is is a Morse Squirrel with a backboiler with a 22mm copper convection loop running through the length of the boat, so it cant really be anything serious.

 

I must admit it doesnt happen all the time, and some times I can go days without it happening, and then itll start again and carry on for a week.

 

I think I just need to put a bleed screw in the back, but at the moment it is just ANOTHER thing to add to my list of things to do, alongside removing all mushrooms from inside the cabin, sorting out the engine coolant etc etc etc etc....

[Tony Brooks]

It was fairly common in the 1970s for those car expansion tanks plus a 21 psi+ pressure cap to be supplied along with calorifiers. They acted as a sort of expansion vessel (as noted earlier).

 

Take the cap off with the pump off and the turn the pump on. My guess is that the tank will fill with water and overflow. If so it is a crude (but effective) domestic hot water expansion vessel.

 

You will note that both the PRV outlet and this outlet run into a 2 pint milk bottle. That suggests no water is being expelled from the domestic system (otherwise we would have had a complaint about wet floors or cupboards) so the domestic hot water has to have an expansion system in place - the tank.

[soldthehouse]

Not in my experience. Air normally results in tiny ticking noises rather than 'knocking'. When most punters use the work 'knocking', they mean something more serious, often the sort of clunking noise that originates from water boiling in the heat source heat exchanger. So Tiggers, can you expand on the knocking noise? I imagine its pretty loud for it to have driven you to consider ripping it all out!

 

When you you notice it? IS your calorifier heated by a solid fuel stove? Does it do it ALL the time or only occasionally?

 

Any water at all discharging from the PRV suggests the system pressure is rising about 3.0 bar, whcih it Bad News and indicates something is wrong.

 

Mike

This is knocking

http://www.youtube.com/watch?v=OilBvKnWM9s

Edited February 20, 2012 by soldthehouse

[Chalky]

I'm amazed nobody has named the make and model of car it has come out of, yet...

 

Oh, if you want to know - generic BMC / Leyland header tank out of Allegro, Marina, MGB etc. They have a bottom exit pipe, the Triumph ones have one out of the top since they're a thermo syphon type of system. Later ones are designed for a through flow to allow the coolant to de-gas more effectively.

Edited February 20, 2012 by Chalky

[blackrose]

I still think that anyone installing a milk cartoon to deal with the discharge from a PRV shows a lack of understanding. Better to address the reason for the discharge in the first place - there will be none from a correctly designed and working system.

 

The milk carton looks empty, so there may have been no discharge at all. I guess they left the milk carton there just in case the system stopped working correctly rather than having a load of hot water all over the floor.

 

The PRV on my calorifier is plumbed overboard.

[MtB]

I think it is trapped air, but it is VERY loud. It is a cross between a knocking and ticking (how unhelpful is that!).

 

I dont have a calorifier, all it is is a Morse Squirrel with a backboiler with a 22mm copper convection loop running through the length of the boat, so it cant really be anything serious.

 

I must admit it doesnt happen all the time, and some times I can go days without it happening, and then itll start again and carry on for a week.

 

I think I just need to put a bleed screw in the back, but at the moment it is just ANOTHER thing to add to my list of things to do, alongside removing all mushrooms from inside the cabin, sorting out the engine coolant etc etc etc etc....

 

Hmmmmm thats definitely a terminal fault. No way of ever fixing it, the only way out is to sell the bote to ME! I'll raise my offer to £30

 

Mike

[carlt]

I think it is trapped air

Have you tried Rennie?

[Tiggers]

Hmmmmm thats definitely a terminal fault. No way of ever fixing it, the only way out is to sell the bote to ME! I'll raise my offer to £30

 

Mike

 

Ha ha, that's a very tempting offer Mike, but I think I may just hold out for a little while longer!

[gillian]

Could it be a way to top up the heating system or is it the pressure release? As another poster noted; it is clean so can't be used too often so is probably ok. I thought it was fairly clever, too..... replace the milk container with another much prettier vessel and you'll never need to worry about it again!

[Roxy]

Had another look at that photograph and..

Are both those rubber hoses going into the milk bottle?

In which case it makes more sense, PRV from calorifier and C/H expansion tank overflow - milk bottle catches drips!

Would expect in that case, a little bit of water in the bottom of the expansion tank?

 

No Robin there is only 1 pipe that goes into this bottle.

 

I have a radiator which barely gets warm (via engine running) if that helps? or is that another topic for me to start...grrrr theres always somthing

 

The milk carton looks empty, so there may have been no discharge at all. I guess they left the milk carton there just in case the system stopped working correctly rather than having a load of hot water all over the floor.

 

The PRV on my calorifier is plumbed overboard.

 

 

 

 

The milk carton has always been empty to my knowledge, however everytime I ran the taps on the sink there seemed to be a wet patch (no rude comments please!) in the middle of the carpet but I put this down to the old tap leaking which it was and was running down the side of the sink unit onto the floor hence why I bought a new one.

[alan_fincher]

Ha ha, that's a very tempting offer Mike, but I think I may just hold out for a little while longer!

You were wise to hold out!.....

 

£50 - How's that sound, then?

[Guest]

We have one in CF, ours is the expansion tank for the central heating

 

 

The Dog House has one too - ours is defo. for the central heating though as we don't have one like that for the engine (Isuzu) as the expansion tank for the engine seems to be incorporated into the system and sits on the engine.... at least that is where I check the level..

 

Our central heating one sits in a side locker in the stern and AFAIK doesn't discharge water anywhere.

[RobinJ]

No Robin there is only 1 pipe that goes into this bottle.

Ok, take 3!

There are 2 flexible connections, convieniently coded with red and blue, I assume they feed the sink taps?

So if the red one is connected to the expansion bottle and the PRV is on the calorifier, why is it not connected to that?

Why is the one with the PRV insulated and the 'hot tap' not?

 

Nw even more confused

[Tiggers]

You were wise to hold out!.....

 

£50 - How's that sound, then?

 

You've got enough boats already!

Edited February 21, 2012 by Tiggers

[blackrose]

I've just added an additional header tank to my engine and connected it via the overflow under the engine's 95 KPa pressure cap. The header tank has a 1.2 bar (120 KPa) pressure cap, so does this mean I shouldn't use it - or I should put a small hole in the cap?

 

My question really is, should the opening pressure on the header tank cap be lower than the engine pressure cap. The only reason I want a cap on the header tank is to stop dirt getting in. Unfortunately the caps aren't interchangeable.

 

Thanks - Mike

Edited February 24, 2012 by blackrose

[Grace and Favour]

This is knocking

 

Ooh - - - put some radseal in yer oil - that'll cure it!

 

 

[Davidss]

I've just added an additional header tank to my engine and connected it via the overflow under the engine's 95 KPa pressure cap. The header tank has a 1.2 bar (120 KPa) pressure cap, so does this mean I shouldn't use it - or I should put a small hole in the cap?

 

My question really is, should the opening pressure on the header tank cap be lower than the engine pressure cap. The only reason I want a cap on the header tank is to stop dirt getting in. Unfortunately the caps aren't interchangeable.

 

Thanks - Mike

You should not run two pressure caps in series or tandem, which is what you are doing.

The pressure cap is designed to vent to the atmosphere or 'free air', so once over 95Kpa that is what your engine cap will do. However, now you have sealed the 'free air' outlet from that cap, so that if the cap does vent, it pressurises the additional header tank. The engine cap now has a new release pressure, as the header tank pressure has to be overcome before the engine cap will release.

If a fault develops the header tank 'could' be pressurised to 120Kpa, this will mean the engine cap won't open until the engine pressure has reached 120 + 95 KPa.

 

What you do depends on which pressure you want your engine cooling system to 'see'. As the caps aren't interchangeable, either remove the inner seal on the engine cap, and leave the overflow cap in place, when your engine will see up to 120KPa, OR, leave the 95KPa cap complete, and remove the seal from the 120KPa overflow cap. The engine will now see 95KPa.

 

HTH

[blackrose]

You should not run two pressure caps in series or tandem, which is what you are doing.

The pressure cap is designed to vent to the atmosphere or 'free air', so once over 95Kpa that is what your engine cap will do. However, now you have sealed the 'free air' outlet from that cap, so that if the cap does vent, it pressurises the additional header tank. The engine cap now has a new release pressure, as the header tank pressure has to be overcome before the engine cap will release.

If a fault develops the header tank 'could' be pressurised to 120Kpa, this will mean the engine cap won't open until the engine pressure has reached 120 + 95 KPa.

 

What you do depends on which pressure you want your engine cooling system to 'see'. As the caps aren't interchangeable, either remove the inner seal on the engine cap, and leave the overflow cap in place, when your engine will see up to 120KPa, OR, leave the 95KPa cap complete, and remove the seal from the 120KPa overflow cap. The engine will now see 95KPa.

 

HTH

 

Yes, of course. Actually now I think about it, it was a stupid question!

 

Thanks

Edited February 24, 2012 by blackrose

[Tony Brooks]

I've just added an additional header tank to my engine and connected it via the overflow under the engine's 95 KPa pressure cap. The header tank has a 1.2 bar (120 KPa) pressure cap, so does this mean I shouldn't use it - or I should put a small hole in the cap?

 

My question really is, should the opening pressure on the header tank cap be lower than the engine pressure cap. The only reason I want a cap on the header tank is to stop dirt getting in. Unfortunately the caps aren't interchangeable.

 

Thanks - Mike

 

 

As long as the only connection between the engine and new expansion tank is via the "overflow" on the engine's filler neck then it will not matter if you have two caps (see below) because the engine cap will open, pressurising the expansion tank, and then as pressure in the engine and expansion tank continues to rise the other cap will open.

 

HOWEVER - On most pressure caps all that seals the cap to the filler neck (if you can call it a seal) is a brass diaphragm so when the engine cap opens the most likely action is for coolant to leak from under the cap.

 

 

Much better to fit a simple cap with a rubbers seal but no spring and valves to the engine filler and the correct pressure cap to the header tank.

 

If you still feel you want a pressure cap on the engine the fit a 5 or 6 PSI one as fitted to Mk1 Fiestas. These had a rubber seal under the cap. Then have the correct filler cap on the expansion bottle.

 

The correct cap for your engine is, presumably, the 95KPa but unless you have soft exhaust manifold end caps (as per BMCs) or soft hoses I doubt the 120KPa one will do any harm.

 

Edited to add:-

 

The scenario given by Davidss will not happen because the caps have two valves. The main one is the pressure valve but the other one is a vacuum break valve that lets air back into the system as the engine cools. (when the pressure outside the cap is higher than that below the cap) so if something very odd happened to allow the engine to depressurise the pressure in the expansion tank will leak back into the engine via the vacuum valve in the cap on the engine.

 

Edited again to add:-

 

25 KPa is just under 4 PSI

Edited February 25, 2012 by Tony Brooks