Setting up a SID shock and having trouble getting an accurate pressure, especially in the negative chamber.

Each time I remove the pump, air escapes. Tried to get around this by estimating the amount lost each time and compensating.

The shock pump I’m using is a Marzocchi – looks like a precision instrument. Any point in buying a better one or do they all suffer from this issue?

The air escaping is the air …from the pump…. not the shock.

All shock pumps are the same, they will all do it.

The air that is escaping is from the hose – which is also under pressure.

Thanks but by reattaching the shock pump it is clear it looses between 10 and 5psi each time the pump is detached.

It’s just the air refilling the shock pump hose from the fork.
I’d stop now before you make it any worse 🙄

The difference in pressure you notice is just the pump repressurising when you reattach it.

Yeah, but isn’t that just air filling the hose from the shock?

Oops too late, what he said!

Rorschach – Member
It’s just the air refilling the shock pump hose from the fork.

+1

Thanks but by reattaching the shock pump it lets a bit of air out of the fork is clear it looses between 10 and 5psi each time the pump is detached.

Thanks but by reattaching the shock pump it lets a minute amount of air out of the fork

I think it might be the attachment of the pump is depressing the valve on the fork and therefore letting a relatively small percentage of the air contained within the fork to escape into the pump. This will result in the apparent pressure decrease that is being observed.

Yes a very small amount of air, but then you add bugger all to pressurise the fork in the first place.
Maybe 10ml at the most for 100+ PSI

I’ve a Magura one, it has a ‘locking’ valve to stop this happening – so yes, its worth it.

No shock pump should release any air from the can unless you tell it to… So if it’s not just refilling the pump, then it’s knackered/not really fit for purpose. But you don’t have to spend a lot, the Beto one that gets sold under about 40 different brand names is spot on and cost me £12 IIRC (branded as Raleigh)

You mean the ‘pressure drop’ observed when you re-attach the shock pump (

air filling the hose from the shock

). 😀
Is it BOGOF tonight?

This review makes in for interesting reading on the subject…

Seems there is a difference of opinion on the air loss phenomenon.

Have opted to get a Topeak as it has ’a provision on the pump chuck to minimize air loss at the Schraeder valve when removing the pump’. Will see.

did any one else read that CC review ? its a joke

scientific – only if you were at clown science

of course the pressures going to change if you keep attaching different items to the valve – each item increases the volume of the chamber !!!!

ARRGGGHHHH

jwmlee, when i first got my dual air revelations i was doing exactly the same as you, reattaching the pump only to find the positive chamber had lost 5 psi and the negative 10 psi. i assumed wrongly that when i removed the pump i was losing the amount stated so my remedy was to increase the pressure by the respective amounts. But the forks were losing a lot of travel as the dual air was obviously not set up right. So i did a lot of googling and from what was explained that it was not detaching the pump from the forks / shocks that lost the air, it was reattaching the pump and the small amount of air filling the pump chamber was the problem.

So pump up to the required PSI and remove. It really is that simple.

Ended up getting a Topeak DXG shock pump with a ‘Pressure-Rite™ connector’ which makes setting proper pressures easy and eliminates air loss when disconnecting.’ Looks like a good quality bit of kit.

Not sure if it is a gimmick or an engenius solution 😀

Not sure if it is a gimmick or an engenius solution

Gimmick, seeing as engenius isn’t a word I’ve ever heard of.

And my magura one, (same design/factory as the topeak one) was rubbish, the hose wasnt sealed properly to the body so you had to do it up tight, and therefore it doesn’t swivel. And then the head parted company from the hose.

Whatever you buy, stick to the one-pump principal and find what pressure (actual, not absolute) works for you.
Gauge reading is just a number.

I have a Magura with the funny adapter and confirm it is rubbish.
I also have a ‘standard’ pump without such frills and it just plain works…every time.

PaulD

I think there is one big factory that makes shock pumps for everyone

When I got my first cheap air fork it didn’t come with a shock pump so I had to buy one – a wrench force i think. Since then I’ve gotten with forks a Fox shock pump and a Rock Shox pump. They are mechanically identical, different colours, different markings on the gauges thats its – exact same layout and castings for the pump.

So buy a cheap one as they seem to be all the same anyway

The smaller the air volume, the larger the pressure loss from that tiny amount of air lost during attachment and/or removal of pump. Car tyres no problem, my bike tyres and forks noticeable.

Cheers to the OP and to the answerers. I’m glad I read this, makes perfect sense. A problem I thought I had has disappeared.

Henceforth, I shall be able to set my fork pressure with less guesswork. And less air, and less need to stop after a while with a “bugger this, they’re a bit stiff” and letting some out with my fingernail.

Does it matter if it’s hot or cold air ?

The temperature of the air in the shock is irrelevant as long as it’s the same temperature of the surrounding air.

Of course, you have to put less air in if you are in the Alps because the surrounding air is thinner.

🙂

Good point,you have to be careful if there is a lot of hot air about 😉

I’ve got the Topeak one that’s in that review with the 2 stage valve. It’s excellent and small enough to carry in a Camelbak on a ride.