On Thu, 01 Sep 2016 10:39:59 -0700, Jeff Liebermann
wrote:

On Thu, 01 Sep 2016 15:29:25 +0700, John B.
wrote:

My experience with repairing gauges has not been wholly satisfactory
mainly because conventional Bourdon Tube gauges usually have
adjustment devices and without a gauge testing service one never knows
whether the repaired gauge is even close to accurate.

Adjusting the typical bourdon tube gauge is difficult, but not
impossible. In general, if there's internal damage, it's easier and
better to replace the gauge. If you're lucky and the gauge has a zero
adjust, then just turn the screw and it should return to zero. Most
small diameter gauges, as found on a bicycle pump, lack easily
accessible adjustments.

Checking the calibration is easy, but you will need to have a known
good pressure gauge available. I built a brass manifold with two
Schrader valves, a Schrader to Presta valve adapter, and a 0-100 lb
digital pressure gauge. If you don't want to buy an accurate pressure
gauge, just install another valve stem and use a known good floor
pump. Then, all you do is pump the tire pump to a value that's in
your operating range, and compare readings between the reference gauge
and your floor pump.

But how do you know that the calibration gauge is reading correctly?
Or your digital gauge, for that matter. A proper testing station will
include a dead weight tester to calibrate the calibration gauge(s) :-)


However, that's probably overkill. Just take two Schrader valve stems
(see below) and attach them together with a 1/4NPT female to female
coupler. Do NOT insert the valves into the stems. Attach two tire
pumps. Pump up either pump and compare gauge readings.

If you need Presta, use an adapter. If you hate adapters, glue two
Presta valve stems together[1].

I'll post a photo when I find mine, but really, it's quite simple to
build.

Brass manifold or tee from the plumbing section of the hardware store.
http://www.provacusa.com/assets/images/4waymanifold.jpg
https://img4.fastenal.com/productimages/440107-131280.jpg

Two gas line pressure test fittings with Shrader valve stems.
https://www.spudtech.com/images/products/airfill.jpg

Schrader to Presta adapter (required if you have a Presta only pump).
http://www.cantitoeroad.com/Valve-Adapter--Schrader-to-Presta_p_263.html

Accurate gauge:
https://www.google.com/search?q=digital+pressure+gauge+1/4+npt&tbm=isch
If you don't like the astronomical prices, something more modest.
https://www.google.com/search?tbm=isch&q=+pressure+gauge+1%2F4+npt


[1]. Careful with this glue method as it could blow apart at high
pressures. Just be VERY careful with the glue job or maybe build a
brass "cage" for the stems using two brass washers and some careful
soldering.
--
cheers,

John B.