How to discharge a rising pumped outlet to avoid freezing.

[Marc Bowers]

Im looking to install a saniflo or similar, with the outlet rising up through a flat roof and into a soil stack above.

The problem is, this obviously poses a frost risk. Ideally I would like to have a method of draining back the contents of the pipework above the roof level once the pumping has ceased to eliminate any chance of freezing.

In my head, I have a tee arrangement with a hinged flap that covers the horizontal branch when the pump is operating but falls back across bottom inlet when the pump stops allowing the water to discharge through the branch and back into the pump below.

The problem is, I've never seen anything like it and don't even know how to start asking google for a solution. Just wondering if any of you chaps/chapess's have any thoughts.

Last resort will be insulation and trace heating.

 

[ShaunCorbs]

Install some frost protection eg heat trace

 

[Marc Bowers]

Install some frost protection eg heat trace

Not sure if you read all of my post but thank you for replying.

 

[ShaunCorbs]

I wouldn’t want to drain human waste into a bucket to stop it freezing

 

[Marc Bowers]

I wouldn’t want to drain human waste into a bucket to stop it freezing

Luckily it’s hand wash basins rather than a macerator, my thoughts were to take the small amount of ‘back-flow’ straight back into the pump unit. For the amount they get used it won’t be much of a problem, but freezing in winter is the greatest concern and if I can solve the problem without loads of unsightly insulation and trace heating, that would be a bonus. I’m sure there is a solution out there, just not one I’ve come across yet. I guess I could do it with some form of zone valve, wired to normally open and linked to the pump switch but I’d rather have a simpler solution if there is one available. I was looking at RPZ valves but the ones I’ve seen diagrams for don’t operate the way I thought.

 

[rpm]

Any water returned to the pumps tank will trigger the pumping cycle to activate. Could sleeve over pipe lagging if you find it unsightly.

 

[Marc Bowers]

Any water returned to the pumps tank will trigger the pumping cycle to activate. Could sleeve over pipe lagging if you find it unsightly.

like the idea of sleeving, I've used downpipes in the past to sleeve the insulation of a mains pipe to an outside tap and it looks far nicer and protects the insulation. Its the trace heating I'm trying to avoid.
As for pump cycling, that all depends on the high and low level switches so thats a controllable factor and isn't of concern.

 

[rpm]

like the idea of sleeving, I've used downpipes in the past to sleeve the insulation of a mains pipe to an outside tap and it looks far nicer and protects the insulation. Its the trace heating I'm trying to avoid.
As for pump cycling, that all depends on the high and low level switches so thats a controllable factor and isn't of concern.

With off the shelf grey water pumps such as a Saniflo the activation level is fixed, or are you going a different route?

 

[Marc Bowers]

With off the shelf grey water pumps such as a Saniflo the activation level is fixed, or are you going a different route?

Nothing is off the table at this point, Im looking at off the shelf and float switch and pump.

The back flow is expected to be a fraction of the discharge of the unit so I am not expecting excessive cycling but its something I'll calculate before making a final purchase decision.

As yet, no-one has any viable solutions to my original question so it might not be an issue anyway. I may have to resort to insulation and trace heating, but I'd love to find an alternative because at the end of the day an empty pipe cannot freeze.

 

[Chuck]

ISTM that by solving one problem (no convenient downpipe) you've created another (freezing) that's harder to solve because, ... physics.

What would you do if the down pipe you have your eye on wasn't there?

TBH, I don't really understand why you have a problem. Surely, once the pump stops the contents of the 'horizontal' pipe are going to run back into the Saniflo or into the downpipe depending on the fall and the pipe won't be full of water in any case? What do the MIs say?

In all matters related to these pumps I defer to @rpm. Take anything he says really seriously.