floor pump at 20 psi when unused?

Hi

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused. It pumps up fine but should I
offset this apparent error when pumping e.g. for 125 psi, pump to 145
psi? It sounds a bit dodgey to me: is it broken, badly calibrated?

ccc rider

On 15 May 2005 03:45:26 -0700, wrote:

Hi

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused. It pumps up fine but should I
offset this apparent error when pumping e.g. for 125 psi, pump to 145
psi? It sounds a bit dodgey to me: is it broken, badly calibrated?

ccc rider

Check tire with a decent tire gauge and then you will know.

I would not want to be riding with 20lbs more air than I had intended.
If you are going to need to purchase a gauge, the nicest one I have
used and own, is the Topeak Smarthead Digital Gauge. The best price
is at Campmor.
http://www.campmor.com/webapp/wcs/st...tId=3037307 2


Life is Good!
Jeff

"Jeff Starr" wrote: Check tire with a decent tire gauge and then you will
know. (clip)
^^^^^^^^^^^^^^^
Of course, that would be the safest thing to do. But I'll bet dollars to
doughnut holes that the problem is in the gauge, and can be solved by
pulling off the needle and repositioning it.

Jeff Starr wrote:
On 15 May 2005 03:45:26 -0700, wrote:

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused.

I would not want to be riding with 20lbs more air than I had
intended.
(snips by me)

Note that the gauge is reading 20psi higher than actual,
so you would be riding with 20psi LESS than intended.
This is not desireable but its less dangerous.

The pump's gauge may just be sticking on the way down.
Checking with a good gauge will tell if you can ignore this.

Ed

On Sun, 15 May 2005 20:30:33 GMT, "Leo Lichtman"
wrote:


"Jeff Starr" wrote: Check tire with a decent tire gauge and then you will
know. (clip)
^^^^^^^^^^^^^^^
Of course, that would be the safest thing to do. But I'll bet dollars to
doughnut holes that the problem is in the gauge, and can be solved by
pulling off the needle and repositioning it.


It would still help to have a separate gauge to calibrate it.


Life is Good!
Jeff

I have the same problem and seems to read true when above 20 lbs compared to
my silca track pump.

"Ed Cory" wrote in message
ups.com...
Jeff Starr wrote:
On 15 May 2005 03:45:26 -0700, wrote:

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused.

I would not want to be riding with 20lbs more air than I had
intended.
(snips by me)

Note that the gauge is reading 20psi higher than actual,
so you would be riding with 20psi LESS than intended.
This is not desireable but its less dangerous.

The pump's gauge may just be sticking on the way down.
Checking with a good gauge will tell if you can ignore this.

Ed

wrote in message
oups.com...
Hi

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused. It pumps up fine but should I
offset this apparent error when pumping e.g. for 125 psi, pump to 145
psi? It sounds a bit dodgey to me: is it broken, badly calibrated?

ccc rider


Maybe it's not able to guage below that?
Is there a stop pin at 20psi?

I say this as my rear shock pump doesn't have the lower numbers on it as
it's geared for 150psi plus.

Easy test - get an inner tube and put a few pumps in, basically see how far
you have to go before it starts to register. If it looks like the tube's
starting to stretch majorly then it's just not going to show below 20psi. If
it starts to register pretty much straight away then it's not calibrated.

HTH.
AndyC

Jeff Starr writes:

I've just been using a Blackburn TPS2 floor pump and noticed it
registers 20 psi when being unused. It pumps up fine but should I
offset this apparent error when pumping e.g. for 125 psi, pump to
145 psi? It sounds a bit dodgey to me: is it broken, badly
calibrated?

Check tire with a decent tire gauge and then you will know.

That will tell you whether your target pressure that you usually ride
is accurately achieved. Most of these non-zero gauges occur when
pumping into a stuck or even closed Presta valve causing pump pressure
to exceed the range of the gauge, thereby bending the bourdon tube,
the heart of such a gauge, beyond yield. Thereafter the tube does not
return the dial to zero and also is no longer as linear as it formerly
was... but close.

http://www.tuchenhagen.de/ndk_website/Tuchenhagen/cmsresources.nsf/filenames/tpia_d+e.pdf/$file/tpia_d+e.pdf

Page 5 shows the workings.

For a quick fix of this condition, gauge shops have a "dial set" that
pulls the needle off its press fit shaft and allows reinstalling it
pointing to zero. As I have mentioned, my pump easily produces over
300 psi although the gauge goes only to 220psi. In days of yore when
I let many bikie friends use the pump my gauge was blasted too often.

http://home.comcast.net/~carlfogel/download/PMP_004.jpg
http://home.comcast.net/~carlfogel/d...d/PUMP_NEW.jpg
http://home.comcast.net/~carlfogel/d...d/PUMP_OLD.jpg

wrote:
As I have mentioned, my pump easily produces over
300 psi although the gauge goes only to 220psi.

http://home.comcast.net/~carlfogel/download/PMP_004.jpg



What vintage is your Silca pump pictured in the website above? I am
guessing mid 1960s. I'm guessing Silca no longer makes anything that
high end today.

Russell Seaton writes:

As I have mentioned, my pump easily produces over 300 psi although
the gauge goes only to 220psi.

http://home.comcast.net/~carlfogel/download/PMP_004.jpg

What vintage is your Silca pump pictured in the website above? I am
guessing mid 1960s. I'm guessing Silca no longer makes anything
that high end today.

It's not a Silca pump. I don't have a logo so I put a Silca label on
it. As you see, I have the design drawings and assembly drawings from
which I and friends made pumps (more than 25 in all) that could
inflate a tubular to 100psi in ten strokes. It was a nice design
challenge and as you see I did two versions, a side-by-side and a
concentric one. Both work well but I prefer the concentric one on
which handle twist does not interfere with pumping. However the
side-by-side has lower sliding friction, having smaller seal diameters.

The crossover port on the side-by-side was a nice feature that remains
completely hidden and was achieved almost by default.