Motorised valve to fit 90mm OD pipe

[Onetap]

The pipe does appear to be galvanised - it's not rusting anyway. I didn't realise you couldn't weld it. Why not? Can't you just grind off the plating? That's going to be a real pain, as the only other option is to get a threaded section to fit the existing joint, and who knows what thread pitch they've used?
I only measured it roughly with a tape. It's about 90mm OD and 80mm bore, and the thread pitch is about 2.25mm. But, is there any guarantee it's a British type anyway?

The zinc galvanizing gives off some toxic fumes, I don't recall what it is, but welders have told me it's nasty stuff. I don't know if it could be fatal, it can certainly make you ill.

Edited to add; It's called metal fume fever. I didn't know that.
http://en.wikipedia.org/wiki/Metal_fume_fever

You can weld the steel, but then the joint is unprotected, unless you can get it hot-dip galvanized after fabrication.

The screwed joint is very probably a BSP thread, 3" BSP has 2.309mm pitch. It is very likely a 3" pipe.
http://en.wikipedia.org/wiki/ISO_228

Viking Johnson fittings should sort it.
http://www.vikingjohnson.com/pdf/maxi_fa.pdf

 

[Softus]

Can't you just grind off the plating?

You seem to think that galvanising is the same thing as plating.

It very much isn't.

 

[ChrisR]

It is really. Galvanising could be done with other metals but it usually means zinc. WHether it's done by plating or dipping, you end up with a coating of zinc on the surface which affords corrosion protection.

I'd still say fix float valves.

DO appreciate that things in Africa sometimes have to be irregular though. Once had the task of stopping immersion heaters in a farm dairy near Mazabuka burning out too quickly. Found the voltage was about 20% too high. It was jacked up to make up for losses in the power supplies to the pumps at the farm's weir, about 5 miles away. Easy, I thought, and drew out a circuit using phase controlled thyristors, standard stuff. Then found that would mean a trip to South Africa to get them!
A visit to the local purveyor of things which passed for technical wasn't very fruitful. So did some tests and came up with the right number and type of light bulbs, which when in series with the heaters, dropped the voltage to the right level. I was dead pleased.
The next morning the light bulbs had all been stolen.
So we put them in the roof of the dairy. Two days later they were gone too, so I worked out what length of what gauge of copper wire would be the right resistance, from the resistivity figure given in an Admiralty Handbook, dated 1930 something. What else would you expect in the middle of Zambia?
The tolerance on the diameter of the copper wire caught me out, but we got the voltage close enough with 50metres of wire looking like a cat's cradle round the dairy roof.
A couple of years later it was still working fine, but I heard that the weight of birds' nests on the wires eventually broke them.
Africa Always Wins!

 

[Softus]

Being somewhat picky, I beg to differ - there's a coating of zinc at the surface, but underlying that is an alloy of zinc and steel.

 

[ChrisR]

Two alloys iirc, and the whole is thicker than electroplated steel, but to the welder it's very much the same. The boiling point of zinc is below steel-welding temperatures, so if you don't grind it off it'll evaporate. Welding current would need to be a bit higher.

 

[Softus]

I think it's the Nitrogen binding that's the concern when welding, but that might be only when MIGing.

 

[ChrisR]

WHat nitrogen binding? The nasty stuff here is ZnO. MIG uses CO2 as a shield gas. Africans up ladders would use stick electrodes.

 

[Softus]

My memory (and reasoning) was wrong about the Nitrogen when MIGing, so I apologise.

I wrote the reply before seeing Onetap's edit, but by "concern" I was referring to WDIK's point about CN compounds, which might still apply if not MIGing.

 

[Norcon]

Since the water tower is about 10m higher, all the water now flows into the tank.

Does the water tower hold its level when the tank valve is opened whilst the pump is operating ?.
Perhaps a non return valve is fitted.

 

[numpty1]

when welding galv use mma,pint of milk before and pint of milk after,stops the fumes doing nasty things to you.large pipe is dipped so coating is inside pipe bore as well grinding off surface does help.

 

[Norcon]

Have heard of the pint of milk before though always treated this with a pinch of salt.
Have done galv welding though grinded as much off as possible and avoided this welding as much as possible.

 

[Softus]

Wouldn't all this risky business be avoided simply by using a mask?

 

[Norcon]

Do you mean potable water and do you want it to remain potable?

Good point. It's feeding a tank that is used for watering the garden, but it's fed from the pipe that fills the house water tank. So yes, it needs to remain potable. It's looking like a secondhand valve is going to be more trouble than it's worth, since I'll have to know what it's been used for.

If the welding is being done on the supply pipe to the garden tank (where the current valve is fitted) then why would the water have to remain potable ?.

 

[numpty1]

Have heard of the pint of milk before though always treated this with a pinch of salt.
Have done galv welding though grinded as much off as possible and avoided this welding as much as possible.

it does work,co i worked for always paid extra for galv welding to cover the cost of milk,todays nanny state requires you to use fume extraction and a suitable mask which makes it a very unpleasant task in warmer weather

 

[Agile]

I doubt that Agile realises how big Africa is.

Zambia and Zim share the Vic falls!

Of course we have not been told where in Zambia this farm is situated.

Of course Chris might be daring to go back to Zambia to update his previous work on the immersion heaters.

I would have used a different technique which would also conserve power. I would have wound the extra length of wire into a coil so as to reduce the length of wire needed. It would only need an impedance of about 4 ohms.

Adding 50m of copper wire is a great temptation to theft even if they can mine copper locally!

That reminds of when I was exploring a deserted switch station in Festaq with totally unprotected 415v conductors all over the place. I heard a strange low pitched noise and looked round to see where it was coming from. I found a growling dog lying in the bottom of one of the switches. Evidently guarding all the exposed parts!

Tony