mushroom valves redundancy?

[Underwater Tourist]

I am not diving cc, but I read how mushroom valves can be delicate on some units and how they can fail or be accidentally damaged.

Is there a reason why back up mushroom valves aren't used? For example, 1 set of valves at one end of the hose near the mouth piece, and another set of valves at the opposite end of the hose that connects to the scrubber.

Feels like a very cheap redundancy to have?

 

[Tracy]

I am not diving cc, but I read how mushroom valves can be delicate on some units and how they can fail or be accidentally damaged.

Is there a reason why back up mushroom valves aren't used? For example, 1 set of valves at one end of the hose near the mouth piece, and another set of valves at the opposite end of the hose that connects to the scrubber.

Feels like a very cheap redundancy to have?

Everything in the breathing loop creates resistance leading to increased work of breathing. Checking the mushroom valves is part of the build on every unit I am aware of. They don't really fail mid dive. Duckweed on the surface can reek havoc on them, it is something to keep in mind when diving in places with it.
There are two check valves in place to ensure gas exchange with each breath. If one fails, the gas still moves through the loop, you just don't get 100% exchange.

 

[LFMarm]

Checking valves and having spares.

 

[Tassi Devil Diver]

Not an issue, stereo checks when building the unit will detect any mushroom valve fault. They are reasonably robust, in the 10 plus years I have been diving CCR I have needed to replace the mushroom valves once.

 

[craig haymaker]

SPEAKING OF WHICH: I added a second mushroom valve (besides the std. BOV valves) into the leaving end of my Exh. loop hose, where it ties into CL Tee. With my BMCL's, if I get into a head down / lower position, I can end up with some gurgling on the exhale side of my BOV (yes, I am very aware of how move that gurgle into the CL). This second mushroom valve greatly reduces this issue! And I feel NO difference in breathing performance.