floor pump at 20 psi when unused?

Quoted message said:

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/stores/servlet/ProductDisplay?memberId=12500226&productId=30373072

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 said:

Quoted message said:

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

Leo Lichtman said:

"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" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Jeff Starr said:

Quoted message said:

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

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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

In article <[email hidden]>,

Quoted message said:

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

Quoted message said:

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.

I've always enjoyed the humour of that Silca label - it's the
sort of thing I would do too. If/when the day comes that I get to
build my own version of this pump, I hope to use the foot, gauge, and
handle of my current Silca Pista. A label for the tube would finish
off the look nicely, but I have no idea where to get one. Of course I
haven't so much as tried contacting Silca for one, either.

Jobst, I'm curious what the stroke length is on your pump. I
tried a back-of-the-envelope calculation for volume a while ago, and
couldn't arrive at 10 strokes.

My Pista takes 28 strokes to 100PSI for my 23mm tires. This
pump has a 28mm ID, and a stroke of 41cm, for a displacement of 252cc.
The Super Pista is 10cm longer, for 314cc displacement. Neglecting
dead-space effects, this would be 23 strokes to 100psi.

For the dimensions in the drawings for your 1.5" pump, the
first stage has an area equivalent to a 33.2mm ID, or 1.4x the area
of Silca's pumps. For the same stroke as a Super Pista, this would
take 16 strokes to fill my tires, and with 28mm tires needing even
more. The 1.625" pump works out to 36.55mm, or ~13 strokes.

Perhaps your stroke length is longer than the Super Pista, but
1.6x taller seems a bit much - the handle would be over 1.6m (5 feet)
high at the top of its stroke! Is this the case, or is there something
else I'm missing?

I haven't worked out the magnitude of dead-space effects, but
would imagine they're comparable for the different pumps. I suppose I
could estimate it for my pump from the declining PSI/stroke.

-Luns

Luns Tee writes:

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

Quoted message said:

Quoted message said:

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

I've always enjoyed the humour of that Silca label - it's the sort
of thing I would do too. If/when the day comes that I get to build
my own version of this pump, I hope to use the foot, gauge, and
handle of my current Silca Pista. A label for the tube would finish
off the look nicely, but I have no idea where to get one. Of course
I haven't so much as tried contacting Silca for one, either.

Quoted message said:

Jobst, I'm curious what the stroke length is on your pump. I tried
a back-of-the-envelope calculation for volume a while ago, and
couldn't arrive at 10 strokes.

Quoted message said:

My Pista takes 28 strokes to 100PSI for my 23mm tires. This pump
has a 28mm ID, and a stroke of 41cm, for a displacement of 252cc.
The Super Pista is 10cm longer, for 314cc displacement. Neglecting
dead-space effects, this would be 23 strokes to 100psi.

The length is optional and in the drawing is it "L" because it was
designed so that the long parts are all the same length, a length of
your choice depending on body height. Most of the pumps built were
24" and four were 25" and one 22". Mine is a long 1-5/8" OD one. The
large diameter pumps were too much pull for some riders, so most were
1.5" OD. All the 25" long pumps were 1-5/8" OD.

Quoted message said:

For the dimensions in the drawings for your 1.5" pump, the first
stage has an area equivalent to a 33.2mm ID, or 1.4x the area of
Silca's pumps. For the same stroke as a Super Pista, this would
take 16 strokes to fill my tires, and with 28mm tires needing even
more. The 1.625" pump works out to 36.55mm, or ~13 strokes.

Quoted message said:

Perhaps your stroke length is longer than the Super Pista, but 1.6x
taller seems a bit much - the handle would be over 1.6m (5 feet)
high at the top of its stroke! Is this the case, or is there
something else I'm missing?

In the cross sectional area noted in the lower left with the
compression ratio and upward pull, you can calculate the effect of the
larger diameter and stroke. I only recall that a Clement criterium
took 10 strokes to 100 psi. Even with my 25mm cross section tires
it's not much more that that to 100. Maybe 14 strokes. Don't overlook
that the entire swept volume of both cylinders (minus wall thickness
and piston rod) is delivered to the tire with each stroke, meanwhile,
there is minuscule dead space.

Quoted message said:

I haven't worked out the magnitude of dead-space effects, but would
imagine they're comparable for the different pumps. I suppose I
could estimate it for my pump from the declining PSI/stroke.

As you can see, the dead space is the screw driver slot in the top
screw, the 0.1" diameter 0.6"long air passage to the check valve and a
small annular space between leather and top screw. This was considered
carefully and is why the check valve is located where it is.

[email hidden]

In article <[email hidden]>,

Quoted message said:

Quoted message said:

Jobst, I'm curious what the stroke length is on your pump. I tried
a back-of-the-envelope calculation for volume a while ago, and
couldn't arrive at 10 strokes.

The length is optional and in the drawing is it "L" because it was
designed so that the long parts are all the same length, a length of
your choice depending on body height. Most of the pumps built were
24" and four were 25" and one 22". Mine is a long 1-5/8" OD one. The
large diameter pumps were too much pull for some riders, so most were
1.5" OD. All the 25" long pumps were 1-5/8" OD.

In the cross sectional area noted in the lower left with the
compression ratio and upward pull, you can calculate the effect of the
larger diameter and stroke.

Stroke doesn't enter what's calculated on the diagrams I've
seen, only areas; there being calculations of force, but not volume.

Actually, I was a little puzzled by the calculations on the
left. The force you give at the end is (CR-1) * 1atm * A, where A is
the area of the downstroke chamber. This forces you give are the
initial push on the _downstroke_, after the low-pressure chamber has
fallen out of the picture.

In pulling upwards, the force on the low pressure cup is CR
times larger than this, for a net pull of (CR-1) times your final
numbers. For your 1-5/8" pump, this is a pull of 36 lbs (rather than
16.4 in the figure). I can appreciate how this would be too much for
some people. 20 lbs for the 1.5" pump sounds much more reasonable.

This high pull force is in part a product of how small your
output chamber is - ease of pushing coming at the expense of
difficulty pulling, for a given delivered volume per unit stroke. I'm
very comfortable with pushing Silca's standard floor pump diameter for
the pressures I need, and don't anticipate a need for 300PSI, so I
intend to use that diameter for my downstroke, and keeping my CR lower
at around 2 to 2.2. I think the Zefal Double-Shot HP is very similar
in dimensions, but its hose comes out the handle intead of the foot.

Quoted message said:

Quoted message said:

For the dimensions in the drawings for your 1.5" pump, the first
stage has an area equivalent to a 33.2mm ID, or 1.4x the area of
Silca's pumps. For the same stroke as a Super Pista, this would
take 16 strokes to fill my tires, and with 28mm tires needing even
more. The 1.625" pump works out to 36.55mm, or ~13 strokes.

Quoted message said:

I only recall that a Clement criterium took 10 strokes to 100 psi.
Even with my 25mm cross section tires it's not much more that that to
100. Maybe 14 strokes.

Ah, I think this is the source of my confusion - I was under the
impression that your 10 strokes to 100psi was for a 28mm tire. What I'm
finding for the Clement criterium is that it's a 21mm tire, in which
case all the numbers make sense.

Quoted message said:

As you can see, the dead space is the screw driver slot in the top
screw, the 0.1" diameter 0.6"long air passage to the check valve and a
small annular space between leather and top screw. This was considered
carefully and is why the check valve is located where it is.

I think this is a little better than Silca's dead space, it
having relatively more volume between the flats of the hex nut and the
leather, and also more overhead from the extra height of the nylock
protrusion. But even with this volume, it's not bad at all. Pumping to
100psi, I just start to see the effects of this with the last 20psi
taking a stroke more than the 20 preceding it.

-Luns

Luns Tee said:

Quoted message said:

Quoted message said:

Jobst, I'm curious what the stroke length is on your pump. I tried
a back-of-the-envelope calculation for volume a while ago, and
couldn't arrive at 10 strokes.

Quoted message said:

Quoted message said:

The length is optional and in the drawing is it "L" because it was
designed so that the long parts are all the same length, a length
of your choice depending on body height. Most of the pumps built
were 24" and four were 25" and one 22". Mine is a long 1-5/8" OD
one. The large diameter pumps were too much pull for some riders,
so most were 1.5" OD. All the 25" long pumps were 1-5/8" OD.

Quoted message said:

Quoted message said:

In the cross sectional area noted in the lower left with the
compression ratio and upward pull, you can calculate the effect of
the larger diameter and stroke.

Quoted message said:

Stroke doesn't enter what's calculated on the diagrams I've
seen, only areas; there being calculations of force, but not volume.

Stroke length figures into how many strokes it takes to 100 psi. The
force calculated is that of the upsroke, not the downstroke, which is
dependent on output pressure that depends on how hard the tire is.

Quoted message said:

Actually, I was a little puzzled by the calculations on the left.
The force you give at the end is (CR-1) * 1atm * A, where A is the
area of the downstroke chamber. This forces you give are the
initial push on the _downstroke_, after the low-pressure chamber has
fallen out of the picture.

Quoted message said:

In pulling upwards, the force on the low pressure cup is CR times
larger than this, for a net pull of (CR-1) times your final numbers.
For your 1-5/8" pump, this is a pull of 36 lbs (rather than 16.4 in
the figure). I can appreciate how this would be too much for some
people. 20 lbs for the 1.5" pump sounds much more reasonable.

I think you are overlooking the cross section ratio of the two areas
which is what gives the force. I may have to look at that again but I
thought I had it right. It isn't obviously simple as I recall.

Quoted message said:

This high pull force is in part a product of how small your output
chamber is - ease of pushing coming at the expense of difficulty
pulling, for a given delivered volume per unit stroke. I'm very
comfortable with pushing Silca's standard floor pump diameter for
the pressures I need, and don't anticipate a need for 300PSI, so I
intend to use that diameter for my downstroke, and keeping my CR
lower at around 2 to 2.2. I think the Zefal Double-Shot HP is very
similar in dimensions, but its hose comes out the handle instead of
the foot.

This pump worked so badly that I never got a good feel for its
operating forces. The one I borrowed seemed to leak on both strokes
to make any assessment useless. The reason they had the hose at the
top is that they didn't consider a hollow piston rod. This is
something historical because no one seems to have discovered that
feature in all the double acting pumps I have seen from times of yore.
The Dunlop #1 pump even went to the complexity of making three
concentric chambers to have the output at the bottom, a useless stubby
brass pump.

As you may recall, I first built a side-by-side pump and got a feel
for the desirable upward force from that and proceeded with that.
After building the 1-5/8" diameter concentric pump, I got complaints
that it pulled too hard so the rest were made 1-1/2" diameter, which
met with user approval. Before the small production run was made.

Quoted message said:

Quoted message said:

Quoted message said:

For the dimensions in the drawings for your 1.5" pump, the first
stage has an area equivalent to a 33.2mm ID, or 1.4x the area of
Silca's pumps. For the same stroke as a Super Pista, this would
take 16 strokes to fill my tires, and with 28mm tires needing even
more. The 1.625" pump works out to 36.55mm, or ~13 strokes.

Quoted message said:

Quoted message said:

I only recall that a Clement criterium took 10 strokes to 100 psi.
Even with my 25mm cross section tires it's not much more that that
to 100. Maybe 14 strokes.

Quoted message said:

Ah, I think this is the source of my confusion - I was under the
impression that your 10 strokes to 100psi was for a 28mm tire. What
I'm finding for the Clement criterium is that it's a 21mm tire, in
which case all the numbers make sense.

Quoted message said:

Quoted message said:

As you can see, the dead space is the screw driver slot in the top
screw, the 0.1" diameter 0.6"long air passage to the check valve
and a small annular space between leather and top screw. This was
considered carefully and is why the check valve is located where it
is.

Quoted message said:

I think this is a little better than Silca's dead space, it having
relatively more volume between the flats of the hex nut and the
leather, and also more overhead from the extra height of the nylock
protrusion. But even with this volume, it's not bad at all.
Pumping to 100psi, I just start to see the effects of this with the
last 20psi taking a stroke more than the 20 preceding it.

Two effects led to the choice of HP piston diameter. The leathers
were available from Silca Impero frame fit pumps and with the higher
starting pressure at the top of the stroke, a smaller diameter than
the available pumps seemed correct. As it is, I don't get the
impression that this wasn't a good choice. A full stroke at higher
starting pressure is different from on that reaches delivery pressure
at the bottom of the stroke. The force curve is higher and flatter
than a one stage pump and this makes the perception of effort.

[email hidden]

Get a new one.