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.

 

[Marc Bowers]

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.

Hi Chuck, If there were no soil stack above there would be no viable option. The situation arrises because an extension has been built on to a property and the existing waste water was routed into a rainwater gulley which went to a soakaway which is now under a concrete floor and apparently blocked so of no use.

Basically a bodged extension built years ago that is now raising its head.

Its a dental practice so 1. money isn't really a problem but 2. disruption to the surgeries is a costly affair, so Im trying to seek a solution that can be installed with minimum disruption but can be relied on all year round.

As for the water in the pipe (I assume you meant vertical, as the horizontal pipe will fall into the soil connection and therefore isn't an issue), the off the shelf pumps have check valves at the unit to stop the back flow into the unit, as a full outlet pipe of water is then very likely to trigger the pump cycling that rpm was warning about. Hence my desire to only empty the top portion of the pipe prone to a freeze risk.

But maybe you're right inso far as that if I make my own float operated sump, I can make it of a size to allow for the water to fully drain back after operation.

 

[IND_Nick]

Could you not introduce a tee into the vertical pumped waste just before it exits the building, put an isolation valve on the horizontal pipe leaving the tee and then drop it back down into the pump/sump arrangement below. When the valve is opened it would just allow the very top/external section of the vertical waste to drain out and doubtful that would re-engage the float valve switch.
As you have said I have never seen this done before, also I don't know if introducing a tee in the vertical would impede the pump, I doubt it.

 

[rpm]

Could you not introduce a tee into the vertical pumped waste just before it exits the building, put an isolation valve on the horizontal pipe leaving the tee and then drop it back down into the pump/sump arrangement below. When the valve is opened it would just allow the very top/external section of the vertical waste to drain out and doubtful that would re-engage the float valve switch.
As you have said I have never seen this done before, also I don't know if introducing a tee in the vertical would impede the pump, I doubt it.

Sorry not sure I follow, will this mean somebody operating the iso valve by hand?

 

[IND_Nick]

Sorry not sure I follow, will this mean somebody operating the iso valve by hand?

Yeah it would need to be manually operated when freezing weather is an issue. Not ideal at all, but just trying to offer an idea, what if it was a gate valve only just opened so 95% goes up and out, then anything left in the top of vertical outside will slowly drip back down.
Again I don't know how badly this will effect the pump. I'm always very careful just to fit these to manufacturers requirements as not good if they go wrong.

 

[Marc Bowers]

Could you not introduce a tee into the vertical pumped waste just before it exits the building, put an isolation valve on the horizontal pipe leaving the tee and then drop it back down into the pump/sump arrangement below. When the valve is opened it would just allow the very top/external section of the vertical waste to drain out and doubtful that would re-engage the float valve switch.
As you have said I have never seen this done before, also I don't know if introducing a tee in the vertical would impede the pump, I doubt it.

Hi IND_Nick. I could but it would involve manually opening the valve after every discharge.

 

[Marc Bowers]

Sorry not sure I follow, will this mean somebody operating the iso valve by hand?

Sorry not sure I follow, will this mean somebody operating the iso valve by hand?

RPM, what are your thoughts on a tee just before the ceiling with a swing style check valve on the 45 degree rise so that gravity holds it open under low pressure situations but the pressure of the pump might push it shut during operation?! Probably needs mocking up at different angles to see what works best but theoretically it’s possible.

 

[rpm]

Well

RPM, what are your thoughts on a tee just before the ceiling with a swing style check valve on the 45 degree rise so that gravity holds it open under low pressure situations but the pressure of the pump might push it shut during operation?! Probably needs mocking up at different angles to see what works best but theoretically it’s possible.

Well since you ask, Is there really a real risk of freezing if you lag and sleeve the pipe and you are wasting time and effort with any secondary check valve.

 

[Marc Bowers]

Well

Well since you ask, Is there really a real risk of freezing if you lag and sleeve the pipe and you are wasting time and effort with any secondary check valve.

I suppose the problem is that I know that putting the rising outlet outside is just bad practice, I can mitigate the issues that might arise by lagging and trace heating but I’m not eliminating them and the worst case scenario with a frozen pipe is that there is a small flood within the building which could damage equipment and possibly put a surgery out of action for a while. I really want a solution that eliminates the risk as much as possible and if that means getting creative with the plumbing or thinking outside the box for a solution, then I’d rather spend a bit of time discussing and thinking through the options rather than just crossing my fingers and hoping for the best. I just can’t believe that there isn’t a solution already out there, it just might not be a typical domestic plumbing solution. I’ll keep looking and thinking for now.

 

[Chuck]

I wouldn't consider a solution that requires the end-users to open and close a valve every time they used the basin when the weather is cold. Firstly, they'll forget / not bother. Secondly, healthcare premises have loads of hygiene rules one of which probably says no touching anything dirty, like a valve handle, after washing your hands. Nor would I consider a home-spun automatic solution that isn't guaranteed to fail-safe.

I've not come across a pump that is suitable but, to be fair, I've never needed to look for one. If you can't find one, I would explain that, in your opinion, the project is going to need to get a builder involved. The extension will need to be modified, or even rebuilt to accommodate the plumbing needed for the basin.

The good news is that dentists are smart people who've done a technical and practical training and will understand the problem. Ultimately, your reputation is worth more than any one job and, if you can't do it properly to your own standard, leave it to someone else.