2" Burrell Kit 21

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Re: 2" Burrell Kit 21

Post  Big Al on Mon 20 Jul 2009, 2:06 am

Bungle

When I went to HOLLOWELL I spoke to Steve about these clack valves. He stated that they would normally be left in the open position. If you close them the injector one or pump one wont be able to top up the boiler with water. The stuff inside the body is like a PTFE and is put in there then drilled out to the size of the valve. The valves do go in with a bit of pressure (I squeezed mine in in the vice) after first clearing out the threads, The second one I put in was a bit loose and leaked past. When the boiler is pressured with the valves open the ball bearing in the chamber should prevent the steam being forced back into the injector/pump. I was therefore not too concerned about the valves not being steam tight providing it does not leak out past the gland at the top.

I did query how the injector or pump forces water into the boiler when it has to overcome the pressure already in the boiler. eg if the boiler is at 75psi how can the injector which is pressurised by the boiler (75psi) overcome the boilers pressure to lift the ball bearings in the clack valves and thus force water in when the are all at the same pressure.

Steve baffled me with the explanation and below is an extract from a website about how they work :-

Injectors work because steam under the same pressure and conditions flows from a contracted nozzle at a much greater velocity than water. The steam cone, or nozzle, regulates the quantity of steam used by the injector. It is both convergent and divergent in order to direct the flow of steam into the combining cone and give it the maximum possible velocity.

The condensation of the steam jet and transfer of its energy to the water takes place in the combining cone which receives the steam and water. In condensing, the steam gives up its velocity to the water, which is then further accelerated by the vacuum in the combining cone caused by the reduction in volume of the steam when condensed by the water. At the inlet end is a jet consisting of a mixture of steam and water, while the outlet end has a jet of hot water flowing at high velocity but very low pressure.

The combining cone is split lengthwise for part of its length and hinged at one end. Should the water supply be interupted the injector stops working as condensation does not occur. Steam when there is no water to condense it can lift the flap and freely escape to atmosphere via the overflow valve until normal water flow is resumed.

The jet passes across a gap after exiting the combining cone and before entering the delivery nozzle. This overflow gap is necessary for disposing of the steam and water before the steam is condensed when starting the injector.

The jet of water is at its maximum velocity as it enters the delivery nozzle, and as it passes through the nozzle and delivery cone its velocity decreases as the bore of the cone increases, so that the pressure will increase until it is sufficient to overcome the boiler pressure and the water can enter the boiler.

When working, the injector would tend draw in air via the overflow pipe, hence the need for a valve on the overflow to prevent this while allowing a free escape for any overflow of water and steam.

That's about as clear as mud as well then!!

Can't wait to get the injector now to see all that working (Ha Ha)

Cheers

Alan

Big Al

Number of posts : 147
Age : 62
Location : Oxford, England (2" Burrell)
Registration date : 2008-06-18

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CLACK VALVES

Post  BUNGLE on Mon 20 Jul 2009, 2:46 pm

THANKS FOR THAT AL, I DID KNOW THAT THEY WOULD REMAIN OPEN ALL THE TIME IN PRACTICE. I HAVE ALSO READ THE EXPLAINTIONS OF HOW INJECTORS WORKS, AND LIKE YOU MOST OF IT WENT OVER MY HEAD !!!!!!! ONE OF THOSE THINGS THAT YOU JUST ACCEPT THAT THATS HOW IT WORKS AND DON'T THINK TO DEEPLY ABOUT I GUESS !!!
SO IT LOOKS LIKE I SHOULD HAVE HAD THE PTFE IN BOTH OF MY CLACK VALVE BODIES, I'LL TALK TO STEVE TOMORROW WHEN I GET CHANCE. AS YOU SAY GUESS IT'S NOT OVERLY IMPORTANT, BUT THEN ON THE OTHER HAND STW WOULDN'T HAVE GONE TO THE EXPENSE OF PUTTING IT THERE IF THEY FELT IT WASN'T NEEDED.

THANKS AL AND TONY FOR COMING BACK TO ME ON THAT.

REGARDS
BUNGLE

BUNGLE

Number of posts : 232
Age : 58
Location : HERTS (2" BURRELL)
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