Might turning a bike with TRP Hy/Rd brakes upside down introduce air in the hydro system? I sometimes turn my bike upside down to pull a wheel off. Internet search reveals nothing about this.

TRP Hy/Rd is a cable actuated hydraulic brake:

Ask @ the TRP brakes website? https://trpcycling.com/contact/

generally the expansion tank has a sealing bladder .. unlike the one on the car firewall ...

Alright I emailed TRP. I didn't know about the sealing blader.

Thanks.

That question always puzzles me. This is a closed system. How could air be introduced in there (or any other hydraulic brake system)?

Merry Sales, Yokozuna brand Motoko disc brakes ; Yokozuna Premium Cables, Housing and Brake Pads are a closed system ..

But you are the pad adjuster, it is not auto compensated..

one thing the HyRd does is eliminate any hose fitting coupling leaks, a common source of air bubbles ..





Magura HS33 Rim brakes are a closed hydraulic system ,, with hoses..
no place for friction heated oil to expand into is needed , because the pads are thick rubber..






,,..

FWIW emailed June 14 to Info@trpbrakes.com

no response yet (June 19)

I don't really understand this stuff, but even if it's a closed system, does that mean there's no air in the system that needs to be worried about?

No, there shouldn't be any air in there. Even if there is, putting the brakes upside down or right side up will not change anything, especially with the HyRds, since there's no hose and nowhere the air can "travel" to.

Think of the different ways they can be mounted. On the fork they are vertical, in the back, they can lay flat, or be at an angle depending where the frame mounts are.

I wouldn't worry about it. Else there'd be a big warning on the box they come in with an arrow "This side up" ;-)

You should call TRP. They are in Ogden Utah and usually answer there phone.

The HY/RD calipers have a rubber bladder under the cap, and work horribly if there's any air in them, so you should be able to turn them upside down without issue. I would actually say that the angle my HY/RD sits on my fork, it's upside down already.

A typical hydraulic braking system is "sealed" as far as something that presses metal pistons through rubber seals can be sealed. If it were perfectly sealed, the fluid would never get fouled, but the pistons also wouldn't be able to move.

Sealed comes in varying degrees.