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  1. #1
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    Silca Super Pista owners: How many PSI per stroke?

    When the pump head is properly seated on a presta valve, how many psi per stroke are you getting? How many strokes does it take you to pump from 0 to 100 psi on a 700x23 tire for example?

    I'm getting about 2.5 psi per stroke on the Super Pista I just purchased and trying to figure out if that's a low figure. I've heard Silca pumps are "fast" (less strokes to reach inflation) and if maintained, last a long time.

    EDIT: How many FULL strokes does it take you to pump from 0 to 100 psi on a 700x23 tire? I acknowledge that psi per stroke will change during inflation. The 2.5 psi per stroke was figured when I went from 80 to 100 psi in 8 full strokes.
    Last edited by cinegabe; 05-05-08 at 08:22 PM.

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    Pwnerer Wordbiker's Avatar
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    I really never counted.

    I just keep going until I get the pressure I need.
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  3. #3
    Senior Member SweetLou's Avatar
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    What's the barometer reading when you pump up your tires? What is the volume of the tire? Are you getting a full load for each pump?

    Too many variables. A pump will push a volume of air into a tube. Different air pressure, size of tire, etc. will change the psi per stroke.

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    I understand there are many variables, but I think it's reasonable to ask whether I am pushing a decent volume of air on each stroke when the pump is being used properly.

  5. #5
    Senior Member SweetLou's Avatar
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    But we can't. There are too many variables. Even between tires of the same size, for example 700x23, will have different volumes this will change the psi. The rim you are using will change the psi per pump. The temperature will change the psi. You are asking an impossible question to answer.

  6. #6
    MFA jjvw's Avatar
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    A "fast" pump will only have a barrel of a larger volume allowing you to push a larger amount of air per stroke.

    Your first pump on a flat tire is going to put the greatest volume of air into the tube. With each successive pump, the volume will decrease as the tire pressure increases.

    You can figure out the math for yours based on your pump, tire, tube, rim, atmospheric conditions, duration of inflation, etc. But if one thing is different on my set of variables, my results will be different.
    Last edited by jjvw; 04-30-08 at 09:47 PM.
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  7. #7
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    Quote Originally Posted by SweetLou View Post
    What's the barometer reading when you pump up your tires?
    What you actually need to know is the ambient pressure and temperature.

    Barometric pressure readings are adjusted to sea level equivilant values, and barometers are calibrated accordingly. Albuquerque International reported a barometric pressure of 30.18" Hg yesterday, but the ambiant pressure at the runway (5200' MSL, give or take) was around 25" Hg...a 20% difference in pressure.

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    Senior Member SweetLou's Avatar
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    Did not know that. Thank you.

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    Quote Originally Posted by jjvw View Post
    With each successive pump, the volume will decrease as the tire pressure increases.
    Why is that?

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    MFA jjvw's Avatar
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    Because you are compressing the air into a smaller volume, thus increasing the pressure. That is why it gets increasingly more difficult to pump air into a tire the higher the PSI becomes. Remember PSI (pressure) stands for Pounds per Square Inch. You are squeezing more air into the same amount of space.

    Put your finger over the end of the pump head and try to "inflate." You will notice that even though you have plugged the end of the pump you can still manage to get a good stroke out of the plunger.
    You are:
    1. compressing the air inside the pump
    2. decreasing the volume of the air inside the pump
    3. increasing the pressure of the air inside the pump

    I will further blow your mind by saying that you are also:

    4. increasing the temperature of the air inside the pump.

    Now release your finger. That whoosh of air is everything returning to "normal" or to the point of equilibrium.
    Last edited by jjvw; 04-30-08 at 11:03 PM.
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  11. #11
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    It's hard to believe it is impossible to know whether my floor pump is working efficiently.

    Anyone have some input that doesn't sound like a cop out?
    Last edited by cinegabe; 05-01-08 at 09:27 AM.

  12. #12
    Senior Member CACycling's Avatar
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    Quote Originally Posted by cinegabe View Post
    Anyone have some input that doesn't sound like a cop out?
    To get a realistic comparison between pumps, you need to fully deflate a tire (or take it down to a fixed pressure), pump it to X psi using Pump A counting how many full strokes it takes, deflate the tire back to the starting point, pump it back to X psi using pump B counting how many full strokes it takes and compare the number of strokes each pump took.

    That's the way I've typically seen pumps compared. Number of full strokes to fill an certain sized tire to X psi.

    Aside from the various atmospheric differences, the number of strokes to get a tire from 110 psi to 120 psi will be far more than the same pump getting the same tire from 10 psi to 20 psi. Try that with YOUR pump on YOUR tire and see if you still think the earlier posts are "cop outs".

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    Quote Originally Posted by CACycling View Post
    That's the way I've typically seen pumps compared. Number of full strokes to fill an certain sized tire to X psi.
    Yeah, and that's what I was asking when I started this thread.

    How well does this particular pump work for you?

  14. #14
    Senior Member GP's Avatar
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    Quote Originally Posted by cinegabe View Post
    It's hard to believe it is impossible to know whether my floor pump is working efficiently.

    Anyone have some input that doesn't sound like a cop out?
    I have the standard Silca. I also have a Supergo FP-3. The Supergo pumps faster. It also has a more comfortable handle. I've never counted the strokes but I've used both pumps for years.

    The Silca is smaller than the Supergo. When I drive to a ride, I carry my stuff in a basket. The Silca fits in the basket. At home I use whichever is closer.

  15. #15
    Senior Member SweetLou's Avatar
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    Quote Originally Posted by cinegabe View Post
    Yeah, and that's what I was asking when I started this thread.

    How well does this particular pump work for you?
    He's saying that you have to use the same wheel and tire to do the comparison. You need two pumps with you to compare them. I can't compare one pump here and you use another wherever you are, it doesn't work.

  16. #16
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    Quote Originally Posted by SweetLou View Post
    He's saying that you have to use the same wheel and tire to do the comparison. You need two pumps with you to compare them. I can't compare one pump here and you use another wherever you are, it doesn't work.
    I don't expect results between us to be the same, but if the pumps are working, they shouldn't be too disparate either.

    Have you even used a Silca Super Pista floor pump?

  17. #17
    Senior Member nick burns's Avatar
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    11.73

  18. #18
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    Quote Originally Posted by jjvw View Post
    Because you are compressing the air into a smaller volume, thus increasing the pressure. That is why it gets increasingly more difficult to pump air into a tire the higher the PSI becomes. Remember PSI (pressure) stands for Pounds per Square Inch. You are squeezing more air into the same amount of space.

    Put your finger over the end of the pump head and try to "inflate." You will notice that even though you have plugged the end of the pump you can still manage to get a good stroke out of the plunger.
    You are:
    1. compressing the air inside the pump
    2. decreasing the volume of the air inside the pump
    3. increasing the pressure of the air inside the pump

    I will further blow your mind by saying that you are also:

    4. increasing the temperature of the air inside the pump.

    Now release your finger. That whoosh of air is everything returning to "normal" or to the point of equilibrium.
    Those statements are true but leave out some important facts about gases. What is a more accurate measure would be the number of moles that you are pumping in with each stroke.

    The Ideal Gas Law relates the volume, temperature, and pressure of a gas, considering the amount of gas present.

    PV=nRT

    V=volume in liters
    n=moles of gas
    P=pressure in atm
    T=temperature in Kelvins
    R is the molar gas constant, where R=0.082058 L*atm*mol-1*K-1.


    P=(nRT)/V

    R is constant
    V is constant
    P is increasing
    T is also increasing
    n is increasing as you pump more in

    P=(nT)(R/V) where (R/V) is constant and nT increasing as you pump in more air and the temp increases.

    The pump cylinder volume is fixed. We'll assume that the heat does not greatly affect the moles of air in that column due to the small amount of time that you the heat can transfer to the air between strokes. The pump is not 100% efficient, there is a little volume of air left at the bottom that is not pushed into the tire. The moles in this not pushed in air increase as the tire pressure increases. There are other losses in the system that eventually the pump can not overcome.

    It is the moles of gas being pushed into the tube on each stroke that is important. The volume is a representation of the moles at a Pressure, Temperature. As the pressure increases, the pumps become less efficient.

  19. #19
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    Quote Originally Posted by nick burns View Post
    11.73
    It's taking me an average of 29 full strokes to go from 0 to 100 psi in my 700x23 clincher.

    11.73 sounds kind of BS, or you've got a really fast pump.

  20. #20
    Senior Member nick burns's Avatar
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    Quote Originally Posted by cinegabe View Post
    It's taking me an average of 29 full strokes to go from 0 to 100 psi in my 700x23 clincher.

    11.73 sounds kind of BS, or you've got a really fast pump.
    Actually it should sound exactly like BS.

  21. #21
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    Quote Originally Posted by nick burns View Post
    Actually it should sound exactly like BS.
    I forgot, you're in Jersey.

  22. #22
    Senior Member SweetLou's Avatar
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    Quote Originally Posted by cinegabe View Post
    I don't expect results between us to be the same, but if the pumps are working, they shouldn't be too disparate either.

    Have you even used a Silca Super Pista floor pump?
    If I am using the same rim and tire as you, then we could get somewhat close in numbers, not the same. You have never said what rim or tire, just 700c x 23. Different rims have different volumes, different tires have different volumes.

    There is just no way to compare different pumps with different wheels. Take your pump to your LBS and compare your pump to theirs.

  23. #23
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    Quote Originally Posted by SweetLou View Post
    There is just no way to compare different pumps with different wheels. Take your pump to your LBS and compare your pump to theirs.
    Ugh, who's comparing different pumps??? I am asking about the Silca Super Pista, the design hasn't changed much over the years.

  24. #24
    Senior Member SweetLou's Avatar
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    You are comparing different pumps, your Silca Super Pista against someone's else. You have to compare the different Pistas to the same wheel.

  25. #25
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    Quote Originally Posted by SweetLou View Post
    You are comparing different pumps, your Silca Super Pista against someone's else. You have to compare the different Pistas to the same wheel.
    Ridiculous. I'm comparing pumps of the SAME model to SIMILAR wheels/tires. You're talking in circles and still haven't said if you have experience with this pump.
    Last edited by cinegabe; 05-05-08 at 08:26 PM.

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