Injector Testing

This topic has 11 replies, 6 voices, and was last updated 27 May 2019 at 17:51 by John Purdy.

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21 May 2019 at 23:35 #410336
John Purdy
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@johnpurdy78347
This is a question for anyone who has built and used an injector test unit to D.A.G. Brown's (Bill Carter's) design. A club member has built one and I have borrowed it to test a couple of injectors. On testing with a known good injector the output pressure gauge only reads 35-40 psi with the injector delivering dry and with boiler pressure of 100 psi applied to the boiler inlet end. The fellow that built it has tested a good many injectors with it, and talking to him he says that is the result he gets and he thinks this is normal. From all I have read I was under the impression that the output pressure gauge should read 5 -10 % above boiler pressure ie. in this case ~105 – 110 psi. I'd be curious to know what other people's experience is.

John
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21 May 2019 at 23:35 #1822
John Purdy
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@johnpurdy78347
22 May 2019 at 00:47 #410340
John Baguley
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@johnbaguley78655
Hello John,

I used a modified version of the Bill Carter test unit which had a simple piston fitted with an O ring. When the injector output pushed the piston against the boiler pressure side the O ring uncovered an outlet port in the bore of the test unit. It seemed simpler to make than the coned seat and coned end on the piston of the Carter design.

When testing an injector I always found that the indicated output pressure was higher than the boiler pressure, sometimes considerably so. I would have expected the Carter unit to give similar results. I am not sure why your, or rather your friends unit should indicate such low output pressures?

John

Edited By John Baguley on 22/05/2019 00:48:58
22 May 2019 at 21:33 #410483
Paul Kemp
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@paulkemp46892
Have you checked the pressure gauge? They have been known to be wrong!

Paul.
22 May 2019 at 22:51 #410498
John Purdy
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@johnpurdy78347
Yes Paul, that's the first thing I did and between 60 and 100 psi is within a couple of psi of a known accurate gauge.

John
22 May 2019 at 23:56 #410502
Paul Kemp
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@paulkemp46892
Ok. Afraid I am not familiar with the device! Any chance it is configured so the gauge reads a differential preassure? That could tie in with the other contribution of often reading "considerably higher than boiler pressure" ?

Paul.
23 May 2019 at 00:28 #410509
John Baguley
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@johnbaguley78655
Hello John,

Just a thought but have you checked to see if you are indeed getting full boiler pressure to the boiler inlet of the test unit? Maybe there is a restriction somewhere that is reducing the pressure? It sounds as though there may be a problem with the test unit.

Paul – I fitted a valve to the outpipe pipe from the test unit so that I could restrict the flow produced by the injector. If you do restrict the output then the pressure should increase. I've had an injector produce double the boiler pressure before now.

John
23 May 2019 at 02:19 #410510
Paul Lousick
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@paullousick59116
John,

You have said that "On testing with a known good injector the output pressure gauge only reads 35-40 psi with the injector delivering dry and with boiler pressure of 100 psi applied to the boiler inlet end. The fellow that built it has tested a good many injectors with it, and talking to him he says that is the result he gets and he thinks this is normal".

This does not sound right and if it is normal and the injectors which he has made previously work OK, then it sounds like the pressure gauge on the tester is NBG. Test again using a different gauge. Or can you swap the 2 gauges for each other. Put the boiler gauge on the tester and vice versa. The results should be the same.

Paul.
23 May 2019 at 07:45 #410520
Brian Baker 2
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@brianbaker2
Greetings, I built & used one of these test valves,and always got higher readings than you suggest.

Can it be that the pressure tapping (pathway) to the gauge is restricted, or in the wrong place?

Regards

Brian
23 May 2019 at 23:04 #410669
John Purdy
Participant
@johnpurdy78347
We've double checked the pressure gauge and it is as accurate as can be expected for a standard commercial gauge

I've had another go with the test unit but before I did I took the valve apart ( with the owner's permission! ) and checked it against the drawings in Brown's book. All dimensions are correct and the pressure gauge and drain pipe connections are in the right place. The only difference is he has replaced the coned seal on the piston with an "O" ring seating against the sharp edge of the inlet bore.

On the test today I tried restricting the outlet of the drain pipe by blocking it with a long piece of wood pressed against the end of the pipe (is that water ever HOT! ). As soon as there was any restriction the indicated pressure rose and when almost completely blocked rose to just under 150 psi, this was with a boiler pressure of about 90psi.

I think I will make a new shuttle valve to the drawing with the cone seating and see if that makes a difference.

John

Edited By John Purdy on 23/05/2019 23:06:10

Edited By John Purdy on 23/05/2019 23:06:48
24 May 2019 at 00:40 #410675
duncan webster 1
Participant
@duncanwebster1
If the gauge is teed in to somewhere where the water has very high velocity, could it be measuring dynamic pressure rather than static? This would explain why restricting the flow ( reducing the velocity) raises the output pressure

Edited By duncan webster on 24/05/2019 00:41:01
27 May 2019 at 17:51 #411178
John Purdy
Participant
@johnpurdy78347
Well the new shuttle valve to the drawing made no difference. Still getting a reading of about 20 psi on the gauge. Also tried two other pressure gauges and they both read essentially the same. The whole unit is now to the drawing. I have measured it all round and all dimensions are within a couple of thou of the drawing dimensions. So why are we getting such a low pressure reading where others are getting a reading of boiler pressure plus?? I'm at a total loss.

John
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