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#4469122 - 07/24/17 05:10 PM Pressure gauge fail
redbone3 Offline

Registered: 06/09/12
Posts: 637
Loc: Reno, NV
I just received a 15 PSIG pressure gauge (China) from ebay. I'm going to use it to monitor the pressure when I pressurize the fuel tank to look for leaks (soapy water method). This test is done at 2 PSIG or less. Knowing the reliability of pressure gauges in general, I checked it's accuracy before using it. The needle didn't move off the peg until 4.5 PSI!! It read 2 PSI with 6.5 PSI was applied. That would likely have damaged my fuel tank. So, a word to the wise: bourdon tube pressure gauges are OFTEN way out of tolerance from the factory. I have found this to be true for both those of US and China origin. Fortunately, repositioning the needle put mine on the money.

Edited by redbone3 (07/24/17 05:10 PM)
2014 Passat Wolfsburg, 1995 Miata.

#4469222 - 07/24/17 06:46 PM Re: Pressure gauge fail [Re: redbone3]
Linctex Offline

Registered: 12/31/16
Posts: 5183
Loc: Waco, TX
The closer the "sweep" of the needle is to 360 degrees, the more accurate it usually is.

Good on you for checking it first.
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

#4469306 - 07/24/17 08:04 PM Re: Pressure gauge fail [Re: redbone3]
Fsharp Offline

Registered: 12/11/15
Posts: 400
Loc: Kentucky
Good to check, I doubt 6.5 PIS would have done too much though. I put 30-40 psi in a tank to de-crumple it. Worked, but my tanks a little rounder now than I would like.

#4469337 - 07/24/17 08:27 PM Re: Pressure gauge fail [Re: redbone3]
L_Sludger Offline

Registered: 10/04/09
Posts: 3947
Loc: Ohio
I think that out of 100 buyers of those gauges, maybe 2 or 3 actually check their accuracy before first use!
too many cars and oil combinations to list in 150 characters or less

#4469351 - 07/24/17 08:36 PM Re: Pressure gauge fail [Re: redbone3]
Silk Offline

Registered: 07/26/03
Posts: 4248
Loc: New Zealand
I have a manometer, but prefer to use vacuum gauges to set the carbs on my bike. Todays job, so calibrated my gauges, different ages and brands, both US brands. So long as the give the same reading they are good enough for the job.

1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - MSL 5/30
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.

#4469405 - 07/24/17 09:15 PM Re: Pressure gauge fail [Re: Linctex]
redbone3 Offline

Registered: 06/09/12
Posts: 637
Loc: Reno, NV
Originally Posted By: Linctex
The closer the "sweep" of the needle is to 360 degrees, the more accurate it usually is.

Good on you for checking it first.

Actually, it's more complicated than that. The most common gauge a mechanic is going to see is a grade B. Grade B gauges are 2% of full scale in the central 50% of the range and 3% of full scale in the first and last 25% of scale. The important part to understand is the full scale designation. For example a 100 PSIG class B gauge would be 3 psi at 10 psig (30% of reading), 2 psi at 50 psi (4% of reading), and 3 psi at 100 psi (3% of reading). If the gauge had just been professionally adjusted it would have been adjusted at midscale to nominal, and would be most accurate there. Unless you have a gauge calibrated, with data, it's a [censored].

Edited by redbone3 (07/24/17 09:16 PM)
2014 Passat Wolfsburg, 1995 Miata.