<VV> Dual Master Cylinder Question

[Bob Gilbert]

Hi,

 

I just acquired a new dual master cylinder from a local parts store which
I'm going to install in my UltraVan. The catalogue entry says it's a 67-69
Camaro unit for drum brakes and it has a 1 inch bore.

 

I read the tech guide articles and looked through Clarks and I'm a bit
curious about the check valves.

 

1) what is their function? 

 

2) How can I tell if my unit has them?  I realise that it probably doesn't
but I'd like to know for sure.

 

3)Are they necessary? The Clarks  catalogue implies no but other sources say
yes

 

Thanks,

Bob