Lavac / Henderson - to vent or not

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Mrstarskydean

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We have a Lavac / Henderson pump heads, I'm just servicing it at the moment and this seems a good time rectify an issue regarding, what I think is, syphoning.

Often our heads fills up with water until the brim of the toilet is reached, only over-spilling as a result of the angle of heal.

It appears that our heads are exactly on the waterline....

We have no vent fitted to the inlet / outlet.

Instructions seen on vents appear to be from the outlet only - is this right?

Is a vent what we need? Maybe this service will solve the issue, in addition to new parts, the whole system is getting a thorough vinegar/ baking soda treatment. The pervious parts appear to date from when Noah was but a lad, testament to the robustness of the system.
 
RupertW said:
Do you know whether it’s the inlet or outlet pipes which are siphoning? I’m assuming the inlet but it might be worth checking as it could be as simple as changing the joker valve? [Note I only know Jabscos but assume Lavacs have joker valves]

But also (on Jabscos) the pump assembly stops the inlet valve sending water to the bowl when properly fitted so it sounds like an odd situation.
Click to expand...
This is nothing like the Jabsco type toilet.
 
Mrstarskydean said:
We have a Lavac / Henderson pump heads, I'm just servicing it at the moment and this seems a good time rectify an issue regarding, what I think is, syphoning.

Often our heads fills up with water until the brim of the toilet is reached, only over-spilling as a result of the angle of heal.

It appears that our heads are exactly on the waterline....

We have no vent fitted to the inlet / outlet.

Instructions seen on vents appear to be from the outlet only - is this right?

Is a vent what we need? Maybe this service will solve the issue, in addition to new parts, the whole system is getting a thorough vinegar/ baking soda treatment. The pervious parts appear to date from when Noah was but a lad, testament to the robustness of the system.
Click to expand...
I wouldn't recommend a vent on the outlet. Give meaning to the expression "getting your own back".
 
From memory I initially also fitted the vent on the outlet but then refitted it to the inlet - my mistake, so wound self amalgamating tape around the outlet pipe which sealed the hole. Reminds me - I'm going to replace the hoses and check the pump this winter as it was definitely harder to pump earlier this year.
 
Tranona said:
The syphoning of seawater is probably because the hole in the bleed valve in the top if the inlet pipe is too small and not breaking the syphon. See the fitting instructions.marinechandlery.com/media/userfiles/lavac.pdf
Click to expand...
Many thanks, yes I'll give the inlet a vent - but is the position of the pipe important? We appear to be sitting on the waterline. I'm concerned that the syphon effect may become terminal.
 
Mrstarskydean said:
Many thanks, yes I'll give the inlet a vent - but is the position of the pipe important? We appear to be sitting on the waterline. I'm concerned that the syphon effect may become terminal.
Click to expand...
The instructions (pp13-15 in the link I posted) say loop the inlet above the waterline. At the top should be the bleed valve which is a little plastic plug. This has an air hole in it that is sized to let just enough air in after you have pumped out to create a reducing vacuum (formed by the seal on the lid) such that when there is enough water in the bowl the vacuum is released. You are either missing this valve or the hole needs enlarging to speed up the rate of air intake.

All explained on p15.
 
Just another thought. The seat seal might be sticking and therefore the vacuum not releasing, although the seal failure is normally NOT sealing and therefor not creating a vacuum. Worth checking though.
 
Mrstarskydean said:
Many thanks, yes I'll give the inlet a vent - but is the position of the pipe important? We appear to be sitting on the waterline. I'm concerned that the syphon effect may become terminal.
Click to expand...

The bowl being on the waterline is not the problem. The lack of a vent in the water inlet pipe is the problem. The inlet pipe should loop up to be above the waterline at all angles of heel, and the vent hole should be at the top of the loop. (Note that you will get greater height compared to the heeled waterline closer to the centre of the boat.)

The vent is provided by a little plastic plug with a tiny hole in it. (Not the standard anti-syphon valve on an inverted U bend you see in chandlers.) A new Lavac comes with 2 different vent plugs, with different sized holes in them. You use the one that gives the your preferred level of water remaining in the bowl after pumping out. You can buy replacement vent plugs from Lavac stockists. I have seen mention on here of people making their own by drilling a tiny hole in the plastic top out of a biro, but as you are not familiar with the original or its operation I recommend you do not attempt this.

Unlike other makes of toilet, most consider that the Lavac does not need a vent in the outlet (and one certainly should not use a simple hole like the Lavac inlet ones, for the reasons alluded to in a previous post!). This is because in practice a Lavac pumps out lot of air along with the waste and water, and this has the effect of breaking the syphon. One does, though, still need to route the outlet pipe above the heeled waterline.

As Tranona suggests, read and follow the Lavac installation instructions and you will be fine.
 
Last edited:
Tranona said:
Just another thought. The seat seal might be sticking and therefore the vacuum not releasing, although the seal failure is normally NOT sealing and therefor not creating a vacuum. Worth checking though.
Click to expand...

Even with the seat seal er, sealed, the vacuum will be broken by the vent in the inlet pipe. It is not dependent on the seat seal 'leaking' at all.
 
PetiteFleur said:
From memory I initially also fitted the vent on the outlet but then refitted it to the inlet - my mistake, so wound self amalgamating tape around the outlet pipe which sealed the hole. Reminds me - I'm going to replace the hoses and check the pump this winter as it was definitely harder to pump earlier this year.
Click to expand...
Yes worth checking. My pump valves and diaphragm backing plate gunged/limescaled up to blockage point this summer
Maintenance would have been much less unpleasant
 
LittleSister said:
The bowl being on the waterline is not the problem. The lack of a vent in the water inlet pipe is the problem. The inlet pipe should loop up to be above the waterline at all angles of heel, and the vent hole should be at the top of the loop. (Note that you will get greater height compared to the heeled waterline closer to the centre of the boat.)

The vent is provided by a little plastic plug with a tiny hole in it. (Not the standard anti-syphon valve on an inverted U bend you see in chandlers.) A new Lavac comes with 2 different vent plugs, with different sized holes in them. You use the one that gives the your preferred level of water remaining in the bowl after pumping out. You can buy replacement vent plugs from lava stockists. I have seen mention on here of people making their own by drilling a tiny hole in the plastic top out of a biro, but as you are not familiar with the original or its operation I recommend you do not attempt this.

Unlike other makes of toilet, most consider that the Lavac does not need a vent in the outlet (and one certainly should use a simple hole like the Lavac inlet ones, for the reasons eluded to in a previous post!). This is because in practice a Lavac pumps out lot of air along with the waste and water, and this has the effect of breaking the syphon. One does, though, still need to route the outlet pipe above the heeled waterline.

As Tranona suggests, read and follow the Lavac installation instructions and you will be fine.
Click to expand...
This is the perfect answer. The key issue is that inlet pipe hole size. The small hole will leave a more full bowl. The large hole leaves a more empty bowl. A blocked or partially blocked hole leaves a very full bowl. My pal didn't like to wait for the vacuum to be lost so he drill a very large hole and used to pump out with one hand whilst his finger on the other hand sealed the hole. Letting go of the hole broke the vacuum instantly and you then lifted the lid.
 
geem said:
This is the perfect answer.
Click to expand...

Thank you, that's very kind.

It wasn't that perfect, as (apart from anything else) I'd missed a critical 'not' from the first sentence of the third paragraph about a vent in the output - (and one certainly should not use a simple hole like the Lavac inlet ones, for the reasons alluded to in a previous post!).

I've corrected this in my post, but the copy of it in your post remains the erroneous original, unfortunately.
 
As well as the biro idea you can just wrap sticky tape around the hole and make your own sized hole with something like a divider point or small drill. And I agree with holding your finger over the hole for a while if you’d like to fill the bowl quickly.
 
LittleSister said:
The bowl being on the waterline is not the problem. The lack of a vent in the water inlet pipe is the problem. The inlet pipe should loop up to be above the waterline at all angles of heel, and the vent hole should be at the top of the loop. (Note that you will get greater height compared to the heeled waterline closer to the centre of the boat.)

The vent is provided by a little plastic plug with a tiny hole in it. (Not the standard anti-syphon valve on an inverted U bend you see in chandlers.) A new Lavac comes with 2 different vent plugs, with different sized holes in them. You use the one that gives the your preferred level of water remaining in the bowl after pumping out. You can buy replacement vent plugs from Lavac stockists. I have seen mention on here of people making their own by drilling a tiny hole in the plastic top out of a biro, but as you are not familiar with the original or its operation I recommend you do not attempt this.

Unlike other makes of toilet, most consider that the Lavac does not need a vent in the outlet (and one certainly should not use a simple hole like the Lavac inlet ones, for the reasons alluded to in a previous post!). This is because in practice a Lavac pumps out lot of air along with the waste and water, and this has the effect of breaking the syphon. One does, though, still need to route the outlet pipe above the heeled waterline.

As Tranona suggests, read and follow the Lavac installation instructions and you will be fine.
Click to expand...
Many thanks for this detailed an informative reply. This forum is a real lifeline. I've fitted the new parts and given the pump a two-day cleaning; note to self clean the whole system/pipes more thoroughly before servicing again. The outlet valve required some extra work to make a seal - I used small rubber 'o' rings between the valve and the front of the pump body around each screw. So far, so good.

The syphon effect remains however, all pipes are looped above the waterline thankfully. What you say makes sense, I will have to drill my own hole in the inlet pipe as there is none - any ideas as to the correct size?
Is this the correct item required? - Lavac TLZ 9251 Bleed Plug Kit for Inlet Hose


Lavac TLZ 9251 Bleed Plug Kit for Inlet Hose
 
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