What is the purpose of this part on the diaphram vacuum pump?

[92EcoDiesel Jetta]

I just pulled a good spare diaphram vacuum pump off of a parts car and looked inside the yellow plastic piece coming off the vacuum port going to the brake booster. There is an arrow on the plastic piece which points to the vac pump. I thought it's a check valve but when I looked inside, there was nothing in there and you can see light through it. I thought it's been messed with  so I looked at the one on my Caddy (pic below) and it's the same!

Anyone know what that piece is for? Seems like it is not needed.

[ORCoaster]

Are these not for taking off more vacuums at different diameter hoses?  Cut the end off and it allows vacuum to be accessible.  That is what I thought but never needed the extra vac so never lopped off the end.

[RabbitJockey]

its for if you had vacuum controlled accessories, like ac

[hillfolk'r]

Yep,extra vacuum ports.and yup cut the ends off an hook em on....like say if your car has AC,it probably would have a hose hooked there
i want the opposite.
i need an" early early"  diesel stubshaft/vacuum pump blockoff,but it needs to fit on an ahu tdi.
im probably gona haveta make one.
hey for giggles keep your old vacuum pump,and grind all the teeth off the gear,cut the top off,weld a nut the shaft or somethin and voila,engine oil pump priming tool
ive seen 1 early diesel oil pump drive/vacuum blockoff/stubshaft in all my years of vw tinkerin.
keep yer eye out for a vane pump,i just think they give a cleaner look and dont blow diaphrams.but hey theres nothing wrong with the old ones either,they worked

[R.O.R-2.0]

its for if you had vacuum controlled accessories, like ac

i hooked the heater up of my mk2 to one of those ports..

you can just pull vacuum from there, being that its the only vacuum source..

[92EcoDiesel Jetta]

.................
hey for giggles keep your old vacuum pump,and grind all the teeth off the gear,cut the top off,weld a nut the shaft or somethin and voila,engine oil pump priming tool

You're kidding right?

I prefer it staying as a working spare. I kinda like the diaphragm pumps because they are easy and cheap to rebuild and work equally well making vacuum as the vane pumps.

[scrounger]

We were driving around in parkas in the last two winters. Turns out the vacuum tube that went from the pump to the heater control had a leak right in the short rubber tube. I suppose the heating coil was heading but the air was not moving past it. Heat is good.

[hillfolk'r]

.................
hey for giggles keep your old vacuum pump,and grind all the teeth off the gear,cut the top off,weld a nut the shaft or somethin and voila,engine oil pump priming tool

You're kidding right?

I prefer it staying as a working spare. I kinda like the diaphragm pumps because they are easy and cheap to rebuild and work equally well making vacuum as the vane pumps.

Not really kidding...i had 3 or 4 layin around.if its the only extra one ya got keep it for a spare.besides an oil pump priming tool can be made easier than that.it depends on how much you wanna overengineer a tool.yea the old vacuum pumps are easy to rebuild,i just like the cleaner look of the newer ones..they both do the same thing though