Vetus H Type Anti Syphon Vent not peeing

[thomd]

I have just installed one of these. Plenty of cooling water coming out the exhaust yet no water at all coming out the top of the Vetus vent into the clear tube to the skin fitting. Have tried blowing down the pipe and its clear.

Any ideas as to why it is not peeing? I assume something is causing suction in the system.

I have a T connector in the antisyphon loop with a feed to water lubricated stern gland which is working fine. I even temporarily blocked this and still no water came out of Vetus vent feed to skin fitting.

I don't think the vent is overly high.

I rang Vetus and they said the vent should always pee something!

Has anyone any suggestions?!

Thanks.

 

[sailorman]

is it the "auto" type. my home made one pee`s all the time as no valve in it

 

[thomd]

is it the "auto" type. my home made one pee`s all the time as no valve in it

No it's not the auto one with a valve. One I've got has no valve but a vent which is supposed to allow a trickle of water to run out and through a skin fitting when engine is running. Yet no water is flowing out of the vent for a reason I can't work out.

 

[boatmike]

The preferred position for the antisyphon is in the pressure side of the supply between pump and engine. Possibly your feed to the stern gland has very little pressure as most water goes to exhaust.

 

[sailorman]

The preferred position for the antisyphon is in the pressure side of the supply between pump and engine. Possibly your feed to the stern gland has very little pressure as most water goes to exhaust.

Thats where i fitted mine when i installed the new engine, the previous perkins 4108 didnt have one fitted

 

[macd]

What revs have you taken the engine to? Mine barely piddles at all until 1400rpm or so.

 

[sailorman]

What revs have you taken the engine to? Mine barely piddles at all until 1400rpm or so.

it would if its fitted after the raw water pump & before the engine

 

[thomd]

Ah ok this makes sense. As I currently have anti syphon loop installed between engine and exhaust it is resulting in a lower pressure of water through the loop compared with installing the loop between pump and inlet to engine. This could be reason nothing is piddling out of anti syphon vent even at high revs.

By changing loop to pressure side this may fix issue and I would also getter a better flow of water to stern gland too.

 

[Tranona]

Where you have it fitted should be OK and is as recommended by Vetus. There is no difference in pressure before and after the engine - it is still the pump that is pumping it. The usual reason for putting it between the pump and the engine (as on my Volvo) is that there is no external hose into exhaust. Can't explain why it does not pee but don't think it is the location.

 

[thomd]

Where you have it fitted should be OK and is as recommended by Vetus. There is no difference in pressure before and after the engine - it is still the pump that is pumping it. The usual reason for putting it between the pump and the engine (as on my Volvo) is that there is no external hose into exhaust. Can't explain why it does not pee but don't think it is the location.

Does the fact it does not pee mean than the anti syphon isnt working? I' assume it will still work if air can flow to the vent when engine is off and as I can blow through it and hose is clear assume it is ok?

 

[boatmike]

Ah ok this makes sense. As I currently have anti syphon loop installed between engine and exhaust it is resulting in a lower pressure of water through the loop compared with installing the loop between pump and inlet to engine. This could be reason nothing is piddling out of anti syphon vent even at high revs.

By changing loop to pressure side this may fix issue and I would also getter a better flow of water to stern gland too.

Thats absolutely correct. The line to the stern gland is after the water has exited the heat exchanger usually and is therefore at a lower pressure despite what trenona says. Pressure is related to flow and diameter of pipe. Most of the flow exits to the exhaust after exiting the HE and usually (depending on what engine you have) the diverted stream to the stern gland is low flow with minimal pressure as most pressure is dissipated in the exhaust. It should still work OK as an antisiphon device where you have it but having a flow of water out of the pee hole keeps it clear and gives peace of mind.

 

[Tranona]

Thats absolutely correct. The line to the stern gland is after the water has exited the heat exchanger usually and is therefore at a lower pressure despite what trenona says. Pressure is related to flow and diameter of pipe.

That is only true if the diameter of the pipe from the HE to the exhaust is substantially different from the diameter of the pipe from the pump to the HE - and I doubt it is. Typically on a small engine they will both be 19 or 25mm.

 

[boatmike]

That is only true if the diameter of the pipe from the HE to the exhaust is substantially different from the diameter of the pipe from the pump to the HE - and I doubt it is. Typically on a small engine they will both be 19 or 25mm.

Sorry but that is wrong. The majority of the water exiting the HE goes directly to exhaust so for a given flow you have to add the diameter of the exhaust pipe to the diameter of any other pipe exiting the HE. Also the flow in the exhaust is assisted by the gas flow. As I said before though it will depend on the engine and where the tapping for the shaft gland is taken from. If its upstream of the exhaust elbow it will be a higher pressure than downstream of it or as sometimes is the case on small diesels, directly from it, but if we are being totally pedantic the total cross sectional area of the heat exchanger will probably be greater than the pipe leading to it so that any pressure tapping from it will be lower pressure than the delivery pipe if the total cross sectional area of all tappings from it are greater than the incoming pipe.

 

[Tranona]

It really depends on the layout and piping. on my Nanni all the water comes out of the HE into a hose the same diameter as the inlet and then into the exhaust. On the Volvo in my other boat it goes direct from the HE into the exhaust so there is no hose. On the Nanni the anti syphon is in this hose, on the Volvo it is between pump and the HE.

The OP says both his Anti syphon and stern tube feed are in between the engine and the exhaust which suggests there is a hose. If the hose is the same size as the inlet there will not be a pressure drop. If the diameter is greater there will be.

 

[thomd]

Thanks all. Yes hose is same diameter between water pump to engine and engine to exhaust. The anti syphon loop is between engine and exhaust. It is a raw water cooled Yanmar 2GM20.

I shall keep investigating.

 

[VicS]

Thanks all. Yes hose is same diameter between water pump to engine and engine to exhaust. The anti syphon loop is between engine and exhaust. It is a raw water cooled Yanmar 2GM20.

I shall keep investigating.

Just a thought or two.

Are you sure your Vetus device is actually the "H" type with no valve? Any chance that you have been supplied with the "V" type by mistake? You'd be able to blow down the pipe but it would not pee.

Does the vent line rise above the antisyphon device by any significant amount?