Vacumn Leak

BobFino

BobFino

Active Member
SILVER Sponsor
Aug 26, 2010
189
Virginia Beach
Boat Info
Sea Ray 550 Sedan Bridge 2005.
Engines
MAN 900
Twin Disc MG-5114
Hello, I am having a problem with my master head. I replaced everything from the floor up in the head, down below I replaced duck valves, I replaced the bellows, I replaced the vacuum switch twice because Dometic and a local repair shop said they are having major problems with their switches because they are no longer made in-house. I checked with a vacuum gauge and the leak is down below. To make matters a little worst while the pump is running I could just slightly touch the vacuum switch and it would turn off and hold the vacuum for hours if not days, meaning it is right at the edge of making enough vacuum. Now it will not go off at all, so the next step is to change the seal at the elbow of the accumulating tank. A little crazy but I am thinking of going ahead and replacing the hose as well, a couple of suggestions were to hook the hose to the new hose and pull through. Sounds too easy, any thoughts would be appreciated especially from somebody who has done it in the past.
 
Are you using No-Flex Digester or Carter's poopy powder??? It solved my cycling problem...
 
Did you replace both o rings on the pump? That is commonly overlooked (specifically the small one sealing the bellows to the pump). If it does hold vacuum....adjust the switch. If there is a leak.....it will continue to cycle after you adjust it.
 
Thank you for the input so far. I am using a digester not Carters. I am told by the local shop and Dometic to never adjust the switch, not sure why but I have not tried to adjust it as of yet. I did replace it twice. My hoses are most likely the original which are old. I would really like to hear from somebody who has done the hose to see what's really involved.
 
I can't speak to the process on your boat, but at that age, I think the hoses are a likely candidate. To test that, you could disconnect at the pump, put a stopper in it, and do the same vacuum test you did previously. Just isolating even more.
 
That is my next step, thank you. Unfortunately, I cannot find any access to the hose, so connecting a new one and pulling through might be my only option.
 
Before you do that......start at the pump/accumulator and disconnect the hose that connects the accumulator to the head and test at the accumulator. If you don't hold vacuum at the accumulator......it is not the hose. This will isolate the accumulator tank, the pressure switch and the pump.

The hose is zip tied down behind the cabinetry. You can't pull it out unless you want to rip out the water lines with it.
 
Thank you and that's what I figured about the line being zip tied.
 
This is the VG4 vacuum accumulator which you should have two on your boat. What John @PlayDate is talking about is putting a rubber stopper in the accumulator (item 13) where the hose connects at item 14. If it pumps down normally and doesn't cycle then the problem is somewhere in the hose to the head or the head.
If on the other hand it continues to cycle then obviously something in the vacuum generator.
The first thing people tend to do is lubricate the duck-bill valves which causes them to squeeze inward when the pvc retainers are tightened and not seal. Get those and the retainer PVC fittings squeaky clean and put it all together dry. Hand tighten only. Same for the duck bill valves under the pump.
I had a vacuum leak that I couldn't find for a year and finally tracked it down to the O-ring under the pump (Item 9). That O-ring seals the same time the two duck-bill valves seal under it. It gets hard and ends up not sealing. It ended up being the most expensive O-ring I've ever purchased.
A cracked bellows will cause the motor to not shut off because it cannot develop a vacuum but it usually makes a mess in the bilge when it fails.
The O-ring (item 22) for the bellows to the top piece can be a bugger to install so check it also.
Last but not least is cracks in the PVC fittings due to over-tightening. The housing (item 24) will easily crack if the fittings are threaded in too tight.

vg4.jpg
 
That is great but I have the VG2. My next step is to remove the hose at the elbow and take a vacuum reading. That will tell me if it is the hose or the seal at the elbow. I did completely rebuild every part in the head above the floor. I also replaced the duck-bill valves. hopefully getting to the elbow seal tomorrow.
Thank you.
 
I just went through the exact same thing. Same symptoms. I threw so many parts at it I gave up and took it in. Long story short, they determined my hose is getting old and weak and it’s not holding shape well and hence loses vacuum. They adjusted the vacuum from 10 pounds to 9 pounds and it supposedly fixed it for now and bought another few years. (I have not picked the boat up yet to confirm)I will replace my hose this winter. Providing its working ok now.
 
I think that's close to where I am at. Changing the hose is not something I would be looking forward to.
 
Rereading your symptoms and the history with the vacuum switch, it sounds like another bad vacuum switch (as mentioned they are touchy). I had similar symptoms as you when I first bought the boat and chased "leaks" all over the place, but in the end it was a bad vacuum switch.

However, I know you said you replaced everything from the floor up, but just confirm you replaced the o-rings on the foot pedal/Ball shaft or the entire ball shaft assembly? There are 2 little o-rings that can produce a very slow leak. The good news is these little buggers can be had at almost any hardware store.

upload_2023-6-18_8-4-8.png
 
BobFino said:
I think that's close to where I am at. Changing the hose is not something I would be looking forward to.
Click to expand...
I am also watching for feedback on hose replacement. I did one in my 270 20+ years ago and it was a bear to pull through. The 40 will be a lot longer pull.
 
K-DUB said:
I am also watching for feedback on hose replacement. I did one in my 270 20+ years ago and it was a bear to pull through. The 40 will be a lot longer pull.
Click to expand...
Ryan @Strecker25 did new hoses on his 410 recently...I forget if he had a thread on it separately or it was in the 400/410 thread. It was a PITA though.
 
BobFino said:
Thank you for the input so far. I am using a digester not Carters. I am told by the local shop and Dometic to never adjust the switch, not sure why but I have not tried to adjust it as of yet. I did replace it twice. My hoses are most likely the original which are old. I would really like to hear from somebody who has done the hose to see what's really involved.
Click to expand...

I have read hundreds of threads on this topic and have never heard of anyone who fixed the leak by adjusting the vacuum switch. And like you stated, the manufacturer is pretty adamant about not messing with.
 
Shaps said:
I can't speak to the process on your boat, but at that age, I think the hoses are a likely candidate. To test that, you could disconnect at the pump, put a stopper in it, and do the same vacuum test you did previously. Just isolating even more.
Click to expand...

How can you check for a leak in the hoses if you disconnect them from the pump?
 
You must log in or register to reply here.

Forum statistics

Threads
113,193
Messages
1,428,278
Members
61,104
Latest member
Three Amigos
Back
Top