Fitting fibreglass cold water tank

[long ironer]

Please, what is the correct placement for the Cu exit pipe to the HW system from a fibreglass cold water tank? This is a standard rectangular shaped tank replacing a galvanized tank.

SFAIUI a fibreglass tank needs to rest on a platform made from (floor)boards carried by joists, rather than just sitting straight on joists as per the old one.

On the old tank the exit CW pipe goes direct out from underneath, but I'm getting conflicting advice as to the correct connection point for the new one. One suggestion is to copy the old tank (ie from underneath), the other is that the pipe should be taken out from the side about 50mm up from the boards.

TIA

[Chris Bacon]

That's OK.

The latter suggestion is best.

[BillP]

The water regulations G16.6 recommendation is that "Where practicable all outlets from a cistern should be taken from the bottom of the cistern."

The idea is to prevent the build-up of debris in the bottom of the tank. Tiny amount of debris that are always present are constantly flushed out and therefore don't lie undisturbed at the bottom.

If your only outlet is the cold water feed to the hot water cylinder, then it should be from the bottom of the tank.

If you have a cold feed for a balanced supply for a shower then this should be from the bottom of the tank, and the cold feed supplying the hot water cylinder should be 50mm above this from the side of the tank.

Bill

[long ironer]

TFT that sounds eminently sensible & optimal from a hydraulic engineering point of view, but what bothered me, mulling it over before posting, was the question of whether a fibreglass tank has the strength to take a hole in its base, especially considering the full weight of water in the tank.

(I assume it is made of fibreglass - if not it is some similar looking plastic.)

[nightjar]

The argument for putting the take-off in the base is that any sediment will be flushed out of the cistern. The argument for putting it 50mm up the side, is that any sediment will settle to the bottom and stay there.

Unless this is the supply the primary circuit of the heating system (it is not entirely clear from your post) the regulations require the outlet to be fitted with a service valve, which may be easier to fit with a side take-off. It also tends to be easier to check a new side connection for leaks once you have done the job. The regulations also require any storage cistern to have a cover that excludes light and insects, adequate insulation and an overflow that excludes insects. The bits you need to achieve that are usually sold as a water byelaw kit, although the water byelaws were replaced by the Water Supply (Water Fittings) Regulations 1999.

Colin Bignell

[Bookworm]

As someone who once had the job of investigating faulty Fibreglass CW tanks for a manufacturer could I suggest that, under no circumstance take the feed from the base of the tank. To do this you would have to drill a hole in the base-board, (essential). The weight of the water will shear the glass fibre between the fitting and the hole in the baseboard. Been there,seen that,hundreds of times.

I investigated causes of hundreds of leaking tanks most were due to incorrect fitting. We had a saying 'If all else fails read the instructions'

I could tell many a tale about faulty installation of CW Tanks.

[long ironer]

instructions? what are those? none came with the tank :-((

be most interested to hear them... but meanwhile TFT JIT - only 5 mins away from starting & doing job the wrong way when your post popped up :-))))

[Chris Bacon]

They must be very poor tanks not to withstand a head of somewhere between 300 and 500mm. I'd suggest that the weight of unsupported pipework is a more likely cause, combined with poor handling/fitting.

[Bookworm]

Story: Had to investigate a tank failure in a refurbished Indian Restuarant in Nottingham once. It appeared the owner was so pleased with the standard of work that he invited all the tradesmen and their wives to a slap-up meal on first night.

Just sat down to main course when the tank above them burst and brought ceiling and tankfull down on them.

Investigation showed that the Plumber had cut the hole for the 22mm Tank Connector with a hacksaw blade very roughly and started a 'notch crack' round the fitting in the Polyethelene.

No payout by manufacturer.

[Bookworm]

It is the weight of the water wot does it! 60 gallons @ 8.34Lbs =

500lbs pressing down on an unsupported area of GRP about 28mm diam (hole) less the diameter of the tank fitting (say 25mm). Punches a lovely neat hole in a couple of months. Been there,seen it at least 50 times.

Good practice with GRP/ Polyethelene or Polypropylene tanks says the WHOLE of the tank base should be supported. Make sure the supporting timber is sound and free from bugs.

Once had a maggot hidden in a timber tank support turn in a wood boring beetle (Anobium Punctatum). Bored its way upwards through the base of a PE Tank. Still got the beetle in a jar somewhere.

[Chris Bacon]

Fortunately, hydraulicals don't work like that! Must've been poor pipework.