Urgent help needed

[alspeed]

On a bit of mare of a job, hoping someone on here can give a fresh perspective, cos i'm running out of ideas.

Scenario is as follows. Dentists Surgery over three floors of a converted terrace, approx 12 basins with mixers and 3 w/c's, hot water is via an
unvented cylinder on the top floor.

I was called in to try and sort out why the taps were spitting badly, mainly the hot, but cold as well, problem started in October last year, when Yorkshire Water did some mains work as another shop on the same parade had complained of low pressure.

At first i suspected the strainer in the cylinder multi function was blocked, but no it was ok, also noticed the cylinder did not have a dedicated cold supply, spoke to the manufacturer who confirmed it would be better to have a dedicated cold feed, especially as the cylinder is on the top floor.

Also spoke to Yorkshire Water, even though pressure seems excellent, who confirmed they had tested the supply to the property recently and all is in order, plenty of pressure and flow.

To test the cylinder starving theory i chucked a hose pipe out of the window and connected directly from the stop tap to the unvented, this seemed to cure the hot problem.... happy days!... also took the pipe into the yard and opened the stop tap, water flowed just as you would expect, plenty of pressure and no fluctuations.
Explained my theory to the custard and they agreed to me running a dedicated supply to the cylinder. Couldn't put a price to the job so we agreed a day rate plus gear. Only slight niggle in my mind was why the system had been working ok up to october.

Have spent the last two days running the pipe ( absolute t*at of a job, all welded vinyl floors and nice decor) however we managed to do it with a minimum of mess, also fitted a pressure reducing valve with gauge just after the stop tap, so i could monitor the pressure. bled all the outlets of air, and all seemed rosy in the garden, taps running nicely with no spitting.... nipped off for some late dinner and to do a couple of gas certs. Came back after a couple of hours expecting to stick my bill in, only to find the system full of air again,:yawn: hot and cold outlets both spitting and banging badly for 30 seconds or so before clearing.

Bottom line seems to be that somehow air is being drawn in.....But how and where ? any ideas folks, cos i'm not going to get paid unless i can sort it:bigcry:

TIA
Al.

 

[GQuigley67]

are all taps spitting ???

 

[alspeed]

Yes all the taps both hot and cold, and it's extreme, the lad drenched himself a couple of times today by opening them too quick.:1eye:

 

[GerrythePlumber]

On a bit of mare of a job, hoping someone on here can give a fresh perspective, cos i'm running out of ideas.

,:yawn: hot and cold outlets both spitting and banging badly for 30 seconds or so before clearing.


TIA
Al.

Why would the cold be "spitting"? Is the cold balanced?

 

[alspeed]

No the cold's not balanced, all cold outlets are fed directly from the main.

 

[GerrythePlumber]

Is there any sign of waterhammer?

 

[Dannypipe]

Is the unvented cylinder a type with an integral air gap or a seperate expansion vessel?

If its a seperate expansion vessel is it hard plumbed in copper or is it attached with a flexi hose?

Also could this be water velocity and could a flow restrictor help? They cost penny's.

 

[GerrythePlumber]

I asked this because i've had problems in the past with the grey coloured expansion vessels. The diaphragm sticks in them sometimes. Also had problems with the combination valve vibrating. You have a remote PRV so that can't be the problem. Usually spitting goes away after the system is full.

 

[alspeed]

No sign of waterhammer.

Cylinder is an RM cylinder with integral expansion.

Don't think a flow restrictor will help, if i go round and bleed the air from all the taps, it all seems to settle down and work fine, but then when its left for
a few hours the problem re-occurs.... it really is like air has entered the system somehow ?

I did think about putting non return valves on all the outlets to eliminate them, or possibly that there is a leak before the stop tap.....clutching at straws really.... proper weird this one is.

 

[Dannypipe]

Attaching the expansion vessel via a flexi hose (despite some manufacturers telling you to do so) can also cause water hammer as the internal diameter is as small as 6mm. Had to change one on an install I did this week. The whole hose was shaking when the vessel emptied. I called manufacturer and they said "Oh we reccomend 22mm connections now" er thanks.

I have some theories with the air, but it only holds up for the hot.

Air is released from the water when it heats...this air could be getting pushed into the expansion vessel if it's the seperate type. When someone opens the tap the air is discharged.

The other thing I would suggest is check valves to each tap to stop air getting dragged in if two taps are opened as one is shut down, if it had a longer run and therefore more pipework (increased friction will mean slightly less pressure at the tap) air could possibly get dragged into the pipework.

Yes I am guessing here, but sounds like you're between a rock and a hard place.

 

[Dannypipe]

Sorry was writing above before you posted the reply.

 

[GerrythePlumber]

Guessing here.
Pressure coming in low, say 3bar. Water rising to top of building, pressure lower at the top.
Someone opens a tap at the bottom. Somone opens a tap at the top.
Water coming out at the bottom robs the tap at the top drawing in air. Is that possible?

 

[GerrythePlumber]

Looks like you need non-return valves to all outlets.

 

[Dannypipe]

Looks like you need non-return valves to all outlets.

My theory is along the same lines. I would try check valves. Also you need to check the baffle plate that forms the air gap is still in one peice.

Recently had a client said tundish was intermitantly dripping, and the water was banging out the taps with a wollop. Turned out there wasn't a baffle plate left, so no air gap in the cylinder. I had to take the lower immersion heater out. Hoover out all the bits of plastic (which had a consistency of candle wax) and then fit a seperate expansion vessel. Also changed the temp/pressure relief valve at same time. That solved the issue.

So in a nut shell. Drain cylinder and take out an immersion heater to check the baffle plate. PS - I had to use a snake cam to check this as the hole in the immersion boss on these super insulated cylinders is very small.

 

[Gray0689]

Did you install the cylinder??

 

[Colin68]

I agree with Gerry, sounds like you've got a tap sucking at the top somewhere 🙁

 

[Kimou]

You say a dentist. During the work the pressure may have dropped. Now correct me if I'm wrong but I'm sure dental unit, with the mouth rinsers, use high velocity air pressure with the water. This may have caused the problem. Isolate the dental units' supplies and see how you fare?
Just a suggestion for elimination.

 

[alspeed]

Thanks to everyone for the replies so far....must admit i'm stumped, and i hate being beaten, especially if it means i don't get paid :thinking:
Deep down I reckon the hot spitting is a red herring, and that the problem is a cold issue, which of course then translates to the hot as its mains fed.

I think on Monday, i'm going to go back armed with a rake of check valves and see if that has any bearing, at least it will eliminate the taps, only downside is i will be throwing more money at the job..... hey ho!

Also forgot to mention, there are two stop taps, 99% of the building is fed from what looks like an old tap, however there is another new looking tap with a meter on it that currently only feeds 1 x w/c and 1 x basin, i might try combining the feeds and see if that has any effect, custard is aware of the stop tap situation, but is of course reluctant to use the metered supply......wonder why:wink_smile:

Edited to answer the above post......., good call, but i already questioned how the water got to the chairs, and its all bottled, they re-fill as necessary, no mains water to the chairs.

Sorry Gray0689, missed your post.... No i didn't install, guess the plumbing was done when the building was converted. Looks ok on the surface, but bodged once you start digging into the fabric. TBH i only got involved to help out a mate, the dentist is a good customer of his, but he only does breakdowns, and didn't have a clue on this one........ My radar was twitching from word go and in any other circumstance i would have walked away......should always listen to the radar !:hand:

 

[kay-jay]

personally i would just try check valves on one outlet, then see if it cures the spitting before wasting time and checkvalves on all outlets before testing only to possibly find out it is some thing else.
if the check valve works then happy days install em at all outlets and job done. if the initial checkvalve doesnt cure that outlet then do as danny says and remove an immersion and check for floating baffle integrity.

KJ

 

[alspeed]

Fair point. will try one tap first....Guess i should also isolate the cylinder and see if the cold taps still spit before venturing further..




=kay-jay;164699]personally i would just try check valves on one outlet, then see if it cures the spitting before wasting time and checkvalves on all outlets before testing only to possibly find out it is some thing else.
if the check valve works then happy days install em at all outlets and job done. if the initial checkvalve doesnt cure that outlet then do as danny says and remove an immersion and check for floating baffle integrity.

KJ[/QUOTE]