Advice on outside drainage

Section62

Kiran said:

RoughNeck said:

..... but the cloakroom waste does drain very slowly and it does block fairly easily. I've no doubt it's due to the lack of fall to the shallow drain and then into the public sewer.

Is this cloakroom connected to a soil stack? You need air to follow water to allow for proper drainage flows. This applies even if you have an acceptable gradient. 

The need for air to get into gravity drainage pipework isn't to allow or encourage flow of the water/solids - gravity alone will take care of that.  Ventilation is needed to equalise air pressure and make sure conditions don't develop which could result in traps being emptied - with the noise and smells that might involve.  The need for adequate ventilation increases with greater falls in the pipework, as the increased velocity of the flow makes it more likely conditions will occur where traps could empty.  With overly-flat falls (which is what it seems likely the OP has) the amount of ventilation won't affect the flow rate.

That said, there should either be an open stack or AAV at the end of that pipe run... but the OP shouldn't expect spending money on having one fitted (if there isn't one already) will make any difference to the rate of flow in the pipe.

RoughNeck

Section62 said:

Kiran said:

RoughNeck said:

..... but the cloakroom waste does drain very slowly and it does block fairly easily. I've no doubt it's due to the lack of fall to the shallow drain and then into the public sewer.

Is this cloakroom connected to a soil stack? You need air to follow water to allow for proper drainage flows. This applies even if you have an acceptable gradient. 

The need for air to get into gravity drainage pipework isn't to allow or encourage flow of the water/solids - gravity alone will take care of that.  Ventilation is needed to equalise air pressure and make sure conditions don't develop which could result in traps being emptied - with the noise and smells that might involve.  The need for adequate ventilation increases with greater falls in the pipework, as the increased velocity of the flow makes it more likely conditions will occur where traps could empty.  With overly-flat falls (which is what it seems likely the OP has) the amount of ventilation won't affect the flow rate.

That said, there should either be an open stack or AAV at the end of that pipe run... but the OP shouldn't expect spending money on having one fitted (if there isn't one already) will make any difference to the rate of flow in the pipe.

I'm learning a lot on here, particularly when I'm not very DIY savvy! In terms of the soil stack, see the photo below. Our cloakroom waste pipe runs into the bottom of it. This is an old photo, but it's the same as what it is today. The stack terminates in the loft. I've always wondered whether this was normal. You can see where the top goes into the loft. I'm assuming because the house is circa 1904, that's why it was done in that way? Ideally the soil stack should terminate outside though, right? So it could go above the guttering for example, and terminate there? And yes, the fascia does need renewing/modernising, but sadly we can't do everything at once

Section62

RoughNeck said:

I'm learning a lot on here, particularly when I'm not very DIY savvy! In terms of the soil stack, see the photo below. Our cloakroom waste pipe runs into the bottom of it. This is an old photo, but it's the same as what it is today. The stack terminates in the loft. I've always wondered whether this was normal. You can see where the top goes into the loft. I'm assuming because the house is circa 1904, that's why it was done in that way? Ideally the soil stack should terminate outside though, right? So it could go above the guttering for example, and terminate there? And yes, the fascia does need renewing/modernising, but sadly we can't do everything at once

That stack isn't original - in that era there were probably separate pipes for the toilet and for the bath/basin/sink, likely of cast iron.

The termination of the stack in the loft isn't necessarily a bad thing - so long as the termination is an air admittance valve (AAV).  It would be an odd thing to take the pipe from the outside (where the termination could be a simple open pipe) into the loft where an AAV were required.  If I were to guess looking at where the pipe enters the wall, I'd say there was a possibility the owner was planning a loft conversion and wanted the soil pipe in the loft to connect a toilet/sink etc.

stuart45

It's also possible when you house was built there were only bedrooms upstairs. Many of the terraced houses of that period had outside toilets and a tin bath.
 

fluffymuffy

RoughNeck said:

This is an old photo, but it's the same as what it is today. 

The wall looks damp where the bathroom toilet waste pipe connects to the stack. Is/was it leaking?

RoughNeck

fluffymuffy said:

RoughNeck said:

This is an old photo, but it's the same as what it is today. 

The wall looks damp where the bathroom toilet waste pipe connects to the stack. Is/was it leaking?

I think it looks darker than it actually is on the photo. They must have had some form of issue here previously as the render is different to the rest of the house and has been patched. I'm pretty sure it's ok now.

Kiran

Section62 said:

Kiran said:

RoughNeck said:

..... but the cloakroom waste does drain very slowly and it does block fairly easily. I've no doubt it's due to the lack of fall to the shallow drain and then into the public sewer.

Is this cloakroom connected to a soil stack? You need air to follow water to allow for proper drainage flows. This applies even if you have an acceptable gradient. 

The need for air to get into gravity drainage pipework isn't to allow or encourage flow of the water/solids - gravity alone will take care of that.  Ventilation is needed to equalise air pressure and make sure conditions don't develop which could result in traps being emptied - with the noise and smells that might involve.  The need for adequate ventilation increases with greater falls in the pipework, as the increased velocity of the flow makes it more likely conditions will occur where traps could empty.  With overly-flat falls (which is what it seems likely the OP has) the amount of ventilation won't affect the flow rate.

That said, there should either be an open stack or AAV at the end of that pipe run... but the OP shouldn't expect spending money on having one fitted (if there isn't one already) will make any difference to the rate of flow in the pipe.

Without air following water you get a turbulent effect on your flow. It won't effect the flow rate but will allow the water, and more importantly the waste suspended in it, to travel at a constant velocity.  Use the analogy of if you have drinking straw full of water at a shallow gradient and you let the water out it will still flow out slowly. If you do the same thing and cover the end of the pipe and let small amounts of air in a series of bursts of air it will be more turbulent. This will lead to solids being deposited on the shallow pipe gradient, not necessarily reducing the flow rate of the pipe 

Section62

Kiran said:

Section62 said:

Kiran said:

RoughNeck said:

..... but the cloakroom waste does drain very slowly and it does block fairly easily. I've no doubt it's due to the lack of fall to the shallow drain and then into the public sewer.

Is this cloakroom connected to a soil stack? You need air to follow water to allow for proper drainage flows. This applies even if you have an acceptable gradient. 

The need for air to get into gravity drainage pipework isn't to allow or encourage flow of the water/solids - gravity alone will take care of that.  Ventilation is needed to equalise air pressure and make sure conditions don't develop which could result in traps being emptied - with the noise and smells that might involve.  The need for adequate ventilation increases with greater falls in the pipework, as the increased velocity of the flow makes it more likely conditions will occur where traps could empty.  With overly-flat falls (which is what it seems likely the OP has) the amount of ventilation won't affect the flow rate.

That said, there should either be an open stack or AAV at the end of that pipe run... but the OP shouldn't expect spending money on having one fitted (if there isn't one already) will make any difference to the rate of flow in the pipe.

Without air following water you get a turbulent effect on your flow. It won't effect the flow rate but will allow the water, and more importantly the waste suspended in it, to travel at a constant velocity.  Use the analogy of if you have drinking straw full of water at a shallow gradient and you let the water out it will still flow out slowly. If you do the same thing and cover the end of the pipe and let small amounts of air in a series of bursts of air it will be more turbulent. This will lead to solids being deposited on the shallow pipe gradient, not necessarily reducing the flow rate of the pipe 

There's no scientific/engineering basis for the assertion above.

Unless the pipe is surcharged (the pipe is flowing full and under pressure) the physics of the flow will be "free surface" (open channel) and gravity will be the main factor.  Open-channel flow can be "turbulent" or "laminar" - but it doesn't need to be either "turbulent" or "laminar" for self-cleansing to occur.  All that is required is for the flow velocity to exceed 0.7m/s (for typical domestic sewage), and that is governed primarily by the fall along the pipe run.  A "constant velocity" is also unnecessary for self-cleansing to occur.

Air doesn't need to "follow" the water for self-cleansing velocity to be achieved, and because the pipe is operating in open-channel conditions if additional air were required to fill the space occupied by the water as it flows away then that normally would be provided by airflow in the pipe in the counter-direction.

The maths of fluid dynamics and open-channel flow are beyond the scope of this forum, all the OP needs to know is that adding a vent to the pipe will make no difference to the probability of them getting blockages. It is one of the 'emergency drain clearing' myths sometimes used to encourage customers to part with their money for additional work.

Your drinking straw analogy isn't applicable, because the straw would be under pressure-pipe conditions rather than open-channel.  Furthermore, the stop-start effect on the flow as you cover/uncover the end of the straw with your finger isn't "turbulence" in the fluid dynamics sense of the word.  The flow would be intermittent or pulsating.

Kiran

It's been a long time since I did fluid dynamics and will hold my hands up and say I didn't enjoy it enough to remember that much of it. What you have written sounds logical and I'm sure what i have to add has no benefit or bearing on the original post. 

That being said, the initial flush be it 4.5, 6 or 9L will unlikely be experiencing open chanel conditions because that volume of water will fill the pipe.  It is at this point that the air benefits the drainage by equalising the pressure and not creating a vacuum effect. Once the initial flush is over and the water flows away, I agree it should be operating under open channel conditions.

Anyway, OP I apologise for adding a post that isn't relevant to you question. Good luck getting a new drainage line in and hope your problem is sorted

RoughNeck

It's all good, and it's all useful stuff. I've contacted the water company so I'll see what I get back from them. Thank you everyone for your comments . I will update as I know more.