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Discuss full bore isolation valve for pressure washer (outside tap ! ) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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steve6710

is there any benefit to having a full bore isolation valve to an outside tap.

the pressure washer that will be attached to it has previously struggled to run of a hose pipe from the kitchen tap and cuts off automatically when it doesnt get enough water.

will the double check valve restrict the flow to a similar rate as the standard isolation valve?

what is the bore on a typical 15mm isolation valve?

does a double check valve reduce flow aswell as stop back flow?
thanks for any advice.......................steve...
 
the check valve will add some resistance. what pressure do you have?
 
not sure what the actual pressure is. all i know is the pressure washer is a little hungry so i want to give it the best flow i can.

its for the sis in law and i am no serious plumber just doing as a favour
 
the hose pipe from the outside tap to the pressure washer will give a big resistance if its a long hose
 
To answer your question on bore, its about 8 to 10mm, I've had no problems with using them providing there is decent pressure. If your washer is pulling more than it can deliver then you will have problems. Full bore will surely help but still comes down to washer and pressure.
 
IMO of you want to improve the flow. I would upgrade the dcv to a standalone dcv 22mm. Even if this means upgrading the pipe size just for the fitting. And fit and old fashioned no dcv bib tap.
 
if i stick with the 15mm dcv is it worth just just buying the dcv bib tap instead to save on extra compression joints in the pipework?
 
if i stick with the 15mm dcv is it worth just just buying the dcv bib tap instead to save on extra compression joints in the pipework?

I find the dcv bib taps very restrictive
 
also over one freezing winter not drained down they tend to fail
 
is there any benefit to having a full bore isolation valve to an outside tap.

the pressure washer that will be attached to it has previously struggled to run of a hose pipe from the kitchen tap and cuts off automatically when it doesnt get enough water.

will the double check valve restrict the flow to a similar rate as the standard isolation valve?

what is the bore on a typical 15mm isolation valve?

does a double check valve reduce flow aswell as stop back flow?
thanks for any advice.......................steve...

assuming that your water pressure is poor then the less restrictions the better, so full bore valve would be better . the double check valve will also reduce pressure as well. Also most pressure washers need around 6m of hose from tap to inlet of pressure washer.
 
Same here.

Can I add. Plumbers need to understand the difference between pressure and flow....I won't go into it in detail, but the pressure of a full bore iso valve is the same as a restricted one...(practically). It's the flow that suffers most when pipe sizing is reduced.
 
I agree, example would be putting thumb on end of hose, you would have more pressure but less flow. What has been said about dcv is all correct, what we can't say is remove it to create flow as this would be against water regs
 
If you're struggling to get enough water to run a pressure washer use a large water butt with a tap on the bottom.
 
down sizing pipes would increase the pressure? using the finger on hose theory or is it more complicated than i am giving it credit for?

there must be a formula out there for starting pressure and pipe bore and altering either will affect the flow and the pressure
 
If you have one of those dreaded diy kits that use a washing machine like hose connected to a self cutting tap, not only do you risk burning out/serious damage to your pressure washer's pump but you will invalidate the manufacturer's guarantee as well. Even the ones in Tool station state "Not suitable for a pressure washer".

The self cutting valve bores a tiny 5-8mm hole in 15mm copper pipe. Over time the diameter of this hole becomes less and less due to corrosion of the steel cutting parts of the valve and whatever scale is in your water supply (lime being a good example).

Pressure washer manufacturers state that 15mm mains fed minimum full bore pipework is required, hence correct installation is via a brass copper or pushfit tee cut into your pipework. I also fit a full bore isolating valve of the lever handle type to allow easy switching off in the Winter months, a double check valve and a GOOD QUALITY bib tap, not a cheap imported one. You get what you pay for so chuck the diy kit in the bin, get a real installation or your pressure washer may also end up in the bin as a expensive diy mistake!
 
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thanks system3, no self cutting tap being used, all soldered and copmression joints only, opted to have the dcv inside the house too as opposed to the dcv bib tap to reduce potential issues with frost affecting the valves, drain cock fitted and full bore isolation lever type too.
makes sense to do it the right way once,
just curious as to where the cut piece of pipe ends up on the self cutting tap? got to cause a problem somewhere at some point!!
 
nine times out of ten it doesn't get cut out completely and just hangs by a tang. the other one it could go anywhere in the system causing allsorts of problems. i only use a cutting tap to drain down where no drain is present and then cut carefully to avoid the small piece detaching.
 
The cutting as Steve says can hang on the pipework, and further adds to the process of catching limescale, rust from the valve blocking the hole, if not one day it will move and work its way into the water supply and could cause mayhem, serious damage to appliances and blockages inside the pipework. They don't tell anyone that on the packaging!

I also use them for drain downs, but remove them, cut out that section of pipework and fit a drain valve when finished.
 
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