I am hosting this for minimate.
He bought a non-S hydro bag from someone, pumped it up and it won't de-pressurise. Is the valve plunger shown in the middle of this pic stuck then?

Comments?

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks for posting Kev. I always wanted to see what was inside.

_________________
The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

A hydro bag's not the sort of thing you could knock up in your workshop, or on a 3D printer either!!

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Kev for posting that photo for me. I've tried pumping it up several times and tried the air compressor on it also. It releases some pressure then takes a day to release some more fluid, but doesn't release all the way. Finding this photo made me wonder if the valve is stuck in position rather than just some crap blocking the hole that connects the chambers ???

I may be wrong but?????
My understanding is that the rubber flap valve flexes when fluid enters from the hose, (movement from the other wheel, providing fluid pressure is high enough to open the valve) and uncovers holes which then allows fluid to enter the RH/lower chamber. (hydro unit on its side in pic)
The retainer piece acts like a spring which tends to keep the valve closed.
The valve shaft doesn't actually move.
Static pressure in the system is about 280 psi - approx. 1.9 Mpa and can reach 400+psi - approx. 2.7 Mpa during a bump.
When the wheel hits a bump and wants to shift fluid out of the RH/lower chamber to the other wheel, the rubber flap valve is held closed and pressure increases in the RH/lower chamber. This pressure is then transferred to the rubber spring part which absorbs some of the bump.
In addition there is a bleed hole which allows some fluid to bypass the closed valve as fluid needs to be transferred to the other hydro unit, for want of a better description, to prepare the other wheel on that side to be ready when it hits the bump.
This all happens in milliseconds.
Its a pretty rough description of how the hydro unit works but it may help.
The BMC black cover workshop manual has a some more info plus some line drawings of the inner workings of the hydro bags and system.
If the pressure is retained in the RH/lower chamber then the bleed hole between the RH/lower chamber and the LH/upper chamber and hose appears to be blocked.
There are 2 basic differences between S and non S bags.
1/ The S rubber spring is thicker where the hose enters as the top of the rubber is only about 1/2" down from the top of the metal case compared to approx. 1" on non S bags.
2/ IIRC the bleed hole diameter between the 2 chambers (not the flap valve holes) in the S bag is smaller than the non S bag.

Winabbey has some info re the difference between the 2 bags in his infinitely large information source.

RonR

_________________
68 build Mk1 Cooper S
72 Clubman GT project. Total restoration required

A good mentor and Larke Hoskins mechanic who worked on minis, 1100s and 1800s when new, told me in the 1970s that the main 'terminal' problem they ever came across in service with hydrolastic systems was when the displacer seized up completely. And it was rare with minis.