Volvo anti-syphon valve

[BigLes]

I have an old Volvo MD5 with sea water cooling. Inside the cockpit locker is an anti-syphon valve that the cooling water passes through. There is a cap nut with a small hole under which is a small thin rubber washer that also has a small hole off-centre. I believe the idea is that when water is being pumped the washer pushes up against the underside of the cap creating a water tight seal, when the engine is off the washer drops and allows air to pass through the two holes and for the water to drain out of the engine.

However on mine whenever the engine is running a 'dome' of water appears on the cap and water trickles down the water pipes, over the engine (not very good for the engine as it's salt water!) and into the bilges. I have bought a service kit (new washer) and fitted it but the problem has started again. Short of buying a new valve (£50 from Volvo) is there any way of solving the problem ie heavier duty washer, an alternative valve assembly etc?

 

[pvb]

The solution...

There is a fairly easy solution to this. (And, firstly, I'm assuming you made sure the top of the valve body was clean and free of deposits before you fitted the new rubber washer, and that you correctly fitted the little copper washer that's part of the service kit).

The solution is to fix a small U-shaped piece of thin copper pipe to the hole on the top of the cap nut. About 6mm pipe is fine. You'll need a piece about 75mm long, bent into a U with about 10mm radius bend. It will need to be soldered or brazed on to the cap nut, and then you need to ensure that the hole in the cap nut is freely open to the pipe. Then refit the cap nut to the valve (you may need to loosen the valve fittings to allow the U-shaped pipe to rotate with the nut). Finally, slip a length of 15mm clear plastic hose over the open end of the little U-shaped tube, and let the other end dangle into the bilge. Fix the plastic pipe to the boat with hose clips so that the U-shaped tube can't come out of the pipe. Now, if there's any leakage from the valve, the water will dribble harmlessly into the bilge, keeping your engine compartment tidier.

 

[mldpt]

Re:Syphon brake

Hi.
My Volvo has a "T" fitted into the bend of the raw water pipe at the top of the loop taking it above the engine and water level, the "T" is fitted int the pipe leaving a small pipe at the top which has a small plastic pipe connected to it taking the water over the side it could be run into the cockpit. When the engine is running and water is being pumped a constant flow is seen running out of the pipe" this is a visual check to see if the water is being pumped" and when the engine stopes the pipe alows air back into the top of the loop and prevents syphoning, hope this helps, my boat had this fitted when new and it seems OK still 14 years later.Mike

 

[BigLes]

Re:Syphon brake

Many thanks for the replies - I think I need to do a bit of modifying to the valve cap.

Les

 

[Guest]

Re:Syphon brake

The secret is to keep the valve housing rubber diaphragm, copper washer clean by soaking in mild Fairy liquid & hot water using a toothbrush. Ensure the copper washer is filed flat on both sides. The idea is not to have a continuous flow of water but an odd drop which we collect in a clear lemonade bottle to see the efficiency of the valve.

Heaven is a boat called . . .

 

[tonyleigh]

Re:Syphon brake

Been meaning to ask almost the same question!!! I have exactly the "bleed" described by PVD but resent the drip into the bilge. A small tonic bottle collects but at higher revs this fills up in an hour. My fitting appears to have no washers - copper of rubber - perhaps they have disintegrated or been removed? Is the kit referred to a Volvo part? Can you help with part number/catalogue description and supplier if this is not a normal Volvo agent item? Many thanks.

 

[Guest]

Why buy a Volvo part? You are well out of the warranty.
Almost any anti-syphon device will fit - dependent solely on the ID of your cooling hose. Most decent chandlers stock them. I think Vetus carry them - look on this (YBW) site. From memory about half the V. rip off price.