Pressure Gauge Dead Weight Tester

I've now gone through the paper indexes for both ME and MEW for the 80's and 90's with no luck. So perhaps it was the one in the Oct 1976 ME that Tony mentioned that I am thinking about. Will have to check in the club library next time I'm down in Victoria, whenever that will be, it's a 498 km round trip.

John

Finding myself awake at this ungodly hour … I had a little dig around t’internet and found this **LINK** which looked promising;

https://modeleng.proboards.com/thread/1996/taunton-model-engineers-magazine

Unfortunately, the embedded link in that post is dead … and currently accessible issues of ‘Oily Rag!’ only go back to 2012

It may, however, be worth contacting Taunton Model Engineers

http://www.tauntonme.org.uk/frontpage.html

MichaelG.

Edited By Michael Gilligan on 29/08/2022 04:04:29

As well as the E.W. Sheppard article (1 Oct 1976, p974) there were two interesting follow up letters on the topic that are noteworthy. ME 7 Jan 1977, p49 and 18 Feb, 1977, p208.

Nealeb jogged my memory ! The injector pump used on the Lister LR, SR,ST and HA series engines, Petter AA and AB and many single or multi cylinder small diesels of the past would be ideal as a starting point for making a dead weight tester. The very accurate piston and a bore vital to success you have ! whilst one could use water as the working fluid, there may be corrosion so the use of diesel fuel or a VERY light oil might be better.Take out the delivery non return valve and even use the injector pipe with an adaptor to your gauge. Remember to set the rack full fuel ! Some fairly simple calculations on piston area and weights applied and you have a dead weight tester ! Noel.

Be aware that the boiler testing regulations require calibrated test equipment. Yes, you can calculate the dimensions you need for a dead weight tester, but you then need to get that calibrated when you've made it. If a boiler goes bang, how are you going to persuade an investigator from HSE or wherever that your testing regime is correct? Have you calibrated your test weights? Have you calibrated the measuring equipment that you used to check the dimensions of your tester?

Your Testing Equipment ought to be traceable to National Standards. Far simpler to get an accredited body to test and calibrate your pressure gauge every couple of years; and it's often as cheap to buy a calibrated gauge new.

Clubs have managed boiler testing for many decades, often relying upon large pressure gauges. I doubt if many possess a dead weight tester. Such concern over extreme scientific accuracy doesn't seem entirely necessary or even desirable, given the enormous safety margin built into the design calculations. So would it really matter if the test pressure was measured to read say 200lb when the actual pressure was say 195 or 205? As long as experienced club testers weed out dodgy looking amateurish boiler making then I think that we can continue to be as safe as we have been for umpteen decades up to the present. I suggest that the majority of boilers are probably professionally made to a good satisfactory standard. One major problem affecting all boilers is that of being choked up with chalk deposits causing overheating of the plates and a shortage of inspection holes as used in full size locomotive boilers. I know of one club that uses modern electronic inspection equipment to view the inside.

Unfortunately the regulations require:

The hydraulic pressure test indicated in Section 10 shall be carried out using a test gauge which has, within the previous two years, been checked and calibrated to within ± 2% either against a currently validated dead weight test apparatus or against other traceable equipment.

Perhaps NAME and SFED should invest in a tester and keep it up to date as a service to clubs

Nigel, in pedantic terms what you say is correct but in practical terms are you not stretching the point a little, certainly considering the ‘guidance’ as quoted by Duncan from the code? Do you think the national standards laboratory would even consider calibrating a 3/4” dia 0 - 150 psi gauge to even 2% when the width of the needle would equal that? If the proposed deadweight tester is checked against a calibrated gauge every 2 years then the spirit and intent of the rules will be met.

But don't they use larger diameter, about 3 or 4 inches, gauges for hydraulic tests, for this very reason?

I can imagine the response from club members on boiler test day when they hear that boiler testing has been cancelled "because our lawyer is off sick."

Or am I just getting cynical these days?

Paul, I am not for one moment suggesting that you send your 3/4" diameter Tich pressure gauge to the National Physical Laboratory for testing. What you do need is that your Club's test equipment is calibrated every two years by somebody who has had their test equipment verified to National Standards. Then you use the Club's gauge to test your boilers and check your own pressure gauge.

If there is a Boiler Incident, there should be no doubt about the testing of the boiler in question. If you haven't complied with the regulations, you can get taken to the cleaners by the injured or bereaved. If you've not complied, then the Insurance Company will happily walk away and leave you to pick up the pieces.

Do you AND the club's Officers & Committee want to be bankrupted and lose your homes (and workshops!) because you've taken a silly short-cut? I don't!

In principle the dead weight tester is so simple that it is almost infalable when properly designed and operated by a person understanding how it works. With the piston diameter checked by a micrometer calibrated to a set of slip gauges, weights checked agaist accurate scales, and a weight to pressure ratio of say 5 being used to set/check a 4" gauge will give an accurate gauge capable of safely testing boilers. The safety factors used in boiler design and construction along with the boiler testing regime have resulted in good safety. That a 3/4" dia gauge is capable of repeatably reading to an accuracy of even 5% I would consider good. Even a 4" gauge set to 2% would require VERY careful reading to reapeatably read to this accuracy !

I fear that perceived precision has overtaken practicallity ! In practical terms I would rather have a test gauge that has been calibrated on a home made dead weight tester than not calibrated at all. The likelyhood of a boiler failing due to scale build up is far more likely yet I see no insistance on an internal examination, YET ! The laws of physics don't change, but hairs can be split ! Noel.

I didn't write the rules, but the rules are there. If you choose to ignore them and have an incident, someone could get hurt, the insurance can refuse to cough up, and in the extreme someone could go to jail. Much easier to just follow the rules. If the rules are thought impractical then get them changed. As I said before, all this would go away if NAME and or SFED had a master gauge or dead weight tester which they got certified every 2 years. This could then be transported round the country from club to club to enable everyone to comply

A point often missed is the actual accident and removal of the victim is usually just the start of a long, stressful and expensive process. Lots of awkward questions get asked: who was in charge, is there a work order, are you insured, can you show all the legal requirements were met, where's the risk assessment and Accident Book, can I see your Heath and Safety Policy, what training was done, and what PPE was provided? Who is your legal advisor in case there is a prosecution or civil claim. Etc. etc. etc.

Any foolish bystander can offer slapdash advice as a way of speeding up work because he won't carry the can if it goes wrong. No problem! People in a position of responsibility have to be much more careful.

Dave

Nigel, I have absolutely zero concerns about our club compliance with the quoted regs. We use an 8” gauge that is checked or calibrated against a master gauge at least every two years by a commercial organisation which issues a cert and a calibration certificate so it is a traceable and auditable process. Prior to this it was checked against a dead weight tester owned by a member of a neighbouring club along with gauges from other local clubs. Again a record of the test was provided for our files. So no shortcuts taken. My understanding was the OP required a method of checking his own model gauges for his own use, there was no mention of issuing his own certification for boiler safety?

My point on the 3/4” gauge was you are testing it against a 2% standard but it is incapable of being guaranteed to be much closer to 10% accuracy itself throughout its range. Model gauges are at best indicators.

Paul.

Having used both dead weight testers for calibrating gauges and pressure transducers and Budenberg dead weight gauges to accurately measure high pressures in the days before we and our customers trusted transducers sufficiently, I'll say that calibrating a dead weight tester every couple of years would be an excercise in stupidity.

The local acceleration of gravity doeasn't change (yes, you do need to correct for that, it isn't 9.80665m/S^2 everywhere), the temperature correction per degree doesn't change (also needed for precision work), the weights don't change over decades if they don't go rusty and the piston dimensions don't change over decades because it's in a perfect environment (precision fit, low load, oil lubricated, low rotational speed).

Added to that, the UKAS lab doing the calibration will be using a dead weight tester with a much longer calibration interval than a couple of years...

This is where you've got to read the rules carefully, not just have a knee jerk reaction. The 2 years refers to the gauge the boiler tester is using, the requirement for dead weight tester is 'currently validated', no time limit.

This kind of discussion always reminds me of the "four rules", applicable to almost any area of modern life.

1. The rules don't make any sense.

2. If you get it wrong, you go to jail.

3. Any questions - see rules 1 and 2.

4. The boys ain't got a sense of humour.

So, so, true.

I think these days clubs are incorporated bodies so the incorporation and not individual members and committee members are liable in the case of lawsuits. I know that is the case in several clubs and community groups I frequent. Otherwise, it would be rather hard to get people to join I up, I should think.

I have to wonder though, have there been cases of people killed or even seriously injured by an exploding model boiler?

When I worked on industrial boilers years ago, small boilers (which were bigger than most models) were exempt from the regulations, inspections, licensed operators etc. It was considered they were not big enough to be dangerous. (Those were different times though, of course. Lawyers had not yet developed their picnics into fully catered banquets at the Ritz. )

Edited By Hopper on 31/08/2022 12:21:16

You may want to read this, Hopper:

**LINK**

https://www.hse.gov.uk/foi/internalops/ocs/100-199/130_8.htm

MichaelG.