Drainage options, advice pls

[WWilts]

Which option would you choose, and why? Is Option 2 workable at all?

[Mr Punter]

The discharge from the pump is very strong.  I would prefer to have it enter the gravity IC straight on so it does not spray around the chamber.

[WWilts]

33 minutes ago, Mr Punter said:

enter the gravity IC straight on so it does not spray around the chamber.

Would this variation on option 2 work? Inspection chamber to break the velocity before discharge into the existing manhole.

The force of the pump discharge suggests that a large radius bend in the MDPE is not fatal.

 

[Mr Punter]

No problem with the bend in the MDPE.  If you put the gravity chamber in around the word "bend" it will be fine. Going to the bigger pipe will help even out the flow.

[saveasteading]

The point about the pressure of water is correct. an uncontrolled release into any chamber will splatter everywhere and possibly erode the chamber.

 

2. is easier and cheaper, as long as the pump is ok with that length. The extra length will reduce the flow somewhat which may be a good thing.

 

how about a) a catch pit, instead of IC, so that the bottom is permanently full of water and the pipe outlet is pointed into it and  is slowed by the standing water.

or  b) pointing the outlet pipe along the gravity pipe.

c) a pump that has enough oomph but not too much.

[WWilts]

8 minutes ago, saveasteading said:

a catch pit, instead of IC, so that the bottom is permanently full of water and the pipe outlet is pointed into it and  is slowed by the standing water.

For avoidance of doubt, this is foul drainage (sewage).

The existing manhole is likely to have a catchpit. Brick and concrete construction (over 100 years old). Not broken into yet. But upstream IC is brick with concrete bench discharging into concrete-embedded pipe (probably clay).

 

11 minutes ago, saveasteading said:

a pump that has enough oomph but not too much.

Good point. Maximum pumping head (level difference) would never exceed 2m. MDPE length from pump to existing manhole would be less than 50m. Pump with 5m head might suffice. Tempted to put the pumping chamber nearer the new dwelling, would increase the MDPE distance by 10m and reduce the force of flow a little bit.

[saveasteading]

3 hours ago, WWilts said:

For avoidance of doubt, this is foul drainage (sewage).

 

Thanks. There is now no doubt. Delete catch pit idea. A very messy idea.

 

If these levels are negative (there is a - which might be a spacer or a minus,) then there is a drop of 0.5m. If positive then there is a rise of 0.5m.

I don't think it matters how much it snakes up and down unless the pipe runs empty for any reason. (which it might if running downhill to the outlet.). 

Pump spec. therefore to be suitable for the  horizontal length and 0.5m rise (or is is fall?) . If it 'just' manages then the pump will be straing and the liwuid willd ribble out. I dont know how much you dare go over.

 

I have found local specialist pump sellers to be very helpful: I guess this an important part of their role, and there is usually one for every area.

[WWilts]

2 hours ago, saveasteading said:

Pump spec. therefore to be suitable for the  horizontal length and 0.5m rise

Yes, pump discharge level will be approx 0.5m BELOW the inlet of the inspection chamber

[Mr Punter]

17 minutes ago, WWilts said:

Yes, pump discharge level will be approx 0.5m BELOW the inlet of the inspection chamber

 

Is the confusion from the AOD abbreviation on the plans?  I have understood this to mean Above Ordnance Datum, which relates to sea level, so most levels I see like this are positive.  I am currently looking at one where the ground floor is 81.60m AOD.  Even next to a tidal river we are 4.00m AOD.

[Dave Jones]

option 2 for sure, you can use a small chamber. It will make the install a lot easier and give you the option of rodding both directions should it ever be needed.

[WWilts]

1 hour ago, Mr Punter said:

Is the confusion from the AOD abbreviation on the plans?

Yes, apologies. AOD reference level in this case is over 40m above AOD. So I should not have introduced this confusion

[WWilts]

1 hour ago, Dave Jones said:

option 2 for sure,

Just to make sure you mean option 2, it is the one where the MDPE has a large radius bend. Either option will include a chamber.

[Dave Jones]

no i meant the bottom picture showing a chamber. 

[WWilts]

4 hours ago, Dave Jones said:

no i meant the bottom picture showing a chamber. 

Thanks, understood. Will installation of curved MDPE be quite difficult?

Agree  that the opportunity to rod both directions (no curve in MDPE) is attractive.

[Mr Punter]

Rods will go round a curve no problem.  You are very unlikely to have a blockage in the pumped section.  The pump will not operate more than once a day.  It is like a fire hose.

[saveasteading]

Have you ruled out a gravity drain? 500mm fall over 50m gives 1:100 which just works.

Putting in a pressure pipe will be cheaper then a gravity drain, and overcome obstacles and topography, but the pump and any storage capacity (in case of brakdown) can be costly and needs maintenance.

[WWilts]

2 hours ago, saveasteading said:

500mm fall over 50m gives 1:100 which just works

Apologies for the confusion. Those were minus signs not hyphens. The house is lower than the manhole invert, not higher. Hence gravity drain ruled out.