Shock pump question

ads678

As a first time shock pump user I'm not sure if i'm doing something wrong.

My shock pump has a housing that screws over the air valve on the shock/fork then another bit that screws in and depresses the pin in the valve to let the air in. The pump works fine in terms of pumping air in but when it comes to disconnecting it form the valve it lets air out as I unscrew it, which means I loose pressure. I tried unscrewing it really fast but it's abit fiddly and I can't do it fast enough to keep the air/pressure in.

It this just because I have a rubbish pump or am I doing something wrong. To be fair it didn't cost much so it could be rubbish.

this is the type i have: http://raleigh.co.uk/ProductType/Produc ... 34&pg=3297

Can any one recomend one that doesn't cost a fortune but works?

nicklouse

have you looked in the FAQs?

sounds totally normal and you are not losing any pressure.

welshkev

sounds normal to me, mine does that and i've got a topeak pocket shock that cost me £35

ads678

Ah, ok, just read the FAQ's.

I was reattaching the pump and getting a lower reading than when I had set the pressure, and therefore assuming I was loosing pressure when disconnecting it.

Cheers for the help.

Chunkers1980

You are. Depends how big all the chambers are. I set mine a few % higher to compensate.

nicklouse

Chunkers1980 wrote:

You are. Depends how big all the chambers are. I set mine a few % higher to compensate.

total bollocks.

chrisga

Thats nice....

jonnyboy66uk

Hiya buddy,

I have the same shock pump made by beta... It aint that good but it does work.

The idea is that you screw onto the valve using the big gold knurled handle and you should have a seperate smaller pinky/red knurled handle on top of this. To pump up ensure that the pinky red handle is screwed firmly into the gold handle, then when you have your pressure unscrew the pinky red handle while holding the gold handle stil, This then releases the air pressure in the pump and line and allows the schreader valve to snap shut quickly. Then you unscrew the gold handle and you should lose no air and everybody is happy.

Hope that helps

Chunkers1980

I didn't want to bite here but..... From Wiki

Presta valves vs. SchraderWhereas Schrader valves are almost universal on car tires, bicycle tires have either Schrader or Presta valves. Both types are good at sealing high pressures. Their chief differences are that Schrader valves are larger and have springs that close the valve except when the pin is depressed. Schrader valves are used in a wide variety of compressed gas and compressed liquid applications.

Compared to Presta valves, Schrader valves used for bicycle tires have a greater diameter, requiring a larger diameter hole in a bicycle rim. While not a concern on wider bike rims, it will weaken a narrow wheel rim, precluding their use on racing bicycles. Another disadvantage of the Schrader is that the air chuck must depress the spring-loaded pin before air can flow during inflation, whereas the Presta valve relies solely on internal air pressure to keep it shut. This means that some air is lost while attaching and detaching pumps to Schrader valves.Screw-on adapters are available at bicycle shops to give a Presta valve the diameter required for using standard air fittings. A rim drilled for Presta valves may be converted to accept Schrader valves by drilling with a 0.328-inch (8.33 mm) bit, though caution must be used.

ads678

How can anyone possibly ever set the right pressure if that is the case?

welshkev

ads678 wrote:

How can anyone possibly ever set the right pressure if that is the case?

not sure :? but is a few PSI either way really gonna make that much difference to us mere mortals?

ads678

I'm fairly heavy, 16st, and i don't want to wreck my shock and i've got no money left after building a FS for the first time.

I wouldn't mind a small pressure loss, but after reconnecting the pump the pressure gauge had gone from 170psi to 100psi and for a lad of my bulk that could be cataustrophic.

cooldad

A minimal amount might come out when you disconnect the pump, but the whoosh you hear is the air in the pump hose, not coming out of the valve. Not enough to worry about - anyway you are setting sag, not pressure.
When you connect, the pump fills up to register the pressure, so the pressure drop is higher.
So keep the pump connected until the sag is right, and you shouldn't have a problem.

ads678

Cheers cooldad that all seems to make sense.