jfkal
Well-Known Member
Is there a danger that water may get siphoned back into the engine from the seal?
Water lubricated stern seals
- Thread starter jfkal
- Start date
charles_reed
Well-Known Member
Do you mean the propellor-shaft seal?
If so the answer is no.
There are, however, certain drawbacks with all shaft-seals and some, like the Deep Sea seal come with user warnings attached.
If so the answer is no.
There are, however, certain drawbacks with all shaft-seals and some, like the Deep Sea seal come with user warnings attached.
Tranona
Well-Known Member
No, the water feed is a bleed off the raw water hose which only runs when the engine runs. When the engine stops, the anti syphon valve opens and any water drains into the stern tube. Flow restarts when the engine starts.
maxi
Well-Known Member
Contrary to the other answers, yes it can.
"If" you have water lubrication taken from the cooling system and "if" you have no antisyphon device then water could syphon back.
If you have no water lubrication from the cooling system then clearly the answer is no.
"If" you have water lubrication taken from the cooling system and "if" you have no antisyphon device then water could syphon back.
If you have no water lubrication from the cooling system then clearly the answer is no.
MoodySabre
Well-Known Member
I have a Tides Marine shaft seal. The water feed loops up above the waterline. I have no anti-syphon and it hasn't been a problem. I do bend the feed pipe and clamp it off with a cable tie when changing the impeller as there is some syphoning with the impeller removed.
vyv_cox
Well-Known Member
It would be an unusual installation in which the engine was lower than the stern gland, I think. Siphoning would therefore seem unlikely. An antisiphon valve, as per Tranona, would solve any potential problem.
GandJ
Member
Water lubricated stern deep sea seals
We have a Manecraft deep sea seal which, from experience, is the best seal for 'our' boat so I am not criticising the seal.
Since adding a t-fitting to feed it [the seal] with pressurised water, as recommended by the manufacturer (between the engine-out and the anti-siphon valve), the raw water cooling system level drops to sea level when the engine is stopped and the boat is sailing -- though not when the boat is upright.
Consequently, we have to turn off the raw water inlet to maintain a level in the raw water strainer as the system does not self-prime. This did not happen when the seal was originally fed from the non-pressurised side (NOT recommended by the manufacturer). See pic which is illustrative and not to scale.
Does any one have any experience of this?
My only idea for a solution is to add a solenoid-valve/tap to the take-off pipe wired in conjunction with the engine so that it opens/closes on engine start/stop. However, finding/making said item is not easy working with the constraints of sea water and generic plumbing sizes/materials.
Surely we cannot be the only boat to suffer from this problem???
We have a Manecraft deep sea seal which, from experience, is the best seal for 'our' boat so I am not criticising the seal.
Since adding a t-fitting to feed it [the seal] with pressurised water, as recommended by the manufacturer (between the engine-out and the anti-siphon valve), the raw water cooling system level drops to sea level when the engine is stopped and the boat is sailing -- though not when the boat is upright.
Consequently, we have to turn off the raw water inlet to maintain a level in the raw water strainer as the system does not self-prime. This did not happen when the seal was originally fed from the non-pressurised side (NOT recommended by the manufacturer). See pic which is illustrative and not to scale.
Does any one have any experience of this?
My only idea for a solution is to add a solenoid-valve/tap to the take-off pipe wired in conjunction with the engine so that it opens/closes on engine start/stop. However, finding/making said item is not easy working with the constraints of sea water and generic plumbing sizes/materials.
Surely we cannot be the only boat to suffer from this problem???
MoodySabre
Well-Known Member
I wouldn't like the idea of an electrically operated item between the raw water inlet and the engine - another thing to go wrong.
On a previous boat the Vetus type strainer was quite high up but it always self-primed - is the strainer lid not sealed with a rubber gasket?
Can you lower the strainer?
How about a one way valve between the inlet and the strainer to stop the water draining down that part of the system - this may give enough head for it to prime.
I take the pressure feed for my Tides seal just after the raw water pump and before the engine
On a previous boat the Vetus type strainer was quite high up but it always self-primed - is the strainer lid not sealed with a rubber gasket?
Can you lower the strainer?
How about a one way valve between the inlet and the strainer to stop the water draining down that part of the system - this may give enough head for it to prime.
I take the pressure feed for my Tides seal just after the raw water pump and before the engine
vyv_cox
Well-Known Member
The pump should self-prime regardless of what is downstream from it, even on first launching, with the strainer and pipework empty.
Possible reasons why it does not:
- As suggested, the strainer seal may be leaking,
- the hoses may be leaking, although this would presumably be noticed,
- the front cover of the pump may be worn, so that the impeller does not contact it,
- the shaft seal may be worn, allowing air into the pump.
I tried MoodySabre's suggestion of a NRV in the line to the strainer when my pump refused to prime, but it was not effective. I carried a bottle of seawater in the engine bilge so that the strainer could be filled to prime the pump. Shortly later the shaft seal failed completely and was replaced, since when all seems to be well.
Possible reasons why it does not:
- As suggested, the strainer seal may be leaking,
- the hoses may be leaking, although this would presumably be noticed,
- the front cover of the pump may be worn, so that the impeller does not contact it,
- the shaft seal may be worn, allowing air into the pump.
I tried MoodySabre's suggestion of a NRV in the line to the strainer when my pump refused to prime, but it was not effective. I carried a bottle of seawater in the engine bilge so that the strainer could be filled to prime the pump. Shortly later the shaft seal failed completely and was replaced, since when all seems to be well.
HunterWanderer
Well-Known Member
Do you have a seacock on the seal?
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