QUIZ:
unscrew the 1" union and there is a .060" hole that necks down to .040" and connects to a ~.135" passage.
who knows what it does?

 

OK, I'll take a guess. Pressure relief?

Glad to see you posting these brain teasers again .

 

No, but here is a clue.
the water pump uses a similar path but it's not in the pump

 

Anti cavitation passage

 

I think that this is what you are describing.

The Saginaw 10 vane power steering pump is a constant displacement pump (i.e. for every revolution of the pump shaft, a nearly fixed amount of oil is sent out the discharge fitting). Without some type of flow control device in the pump, this could result in 10 to 15 gallons of oil per minute at say 5000 rpms (your steering gear only needs 2 or 3 gallons of flow).

There is a very small port that communicates off to the side from the orifice in the discharge fitting. Higher velocity through the orifice translates to lower pressure. This port takes that low pressure signal and sends it back through a passage inside the pump. That passage leads to the chamber behind the flow control valve. There is a spring in that chamber always pushing the flow control valve toward the discharge fitting. Lower pressure behind the flow control valve and higher pressure on the discharge fitting side of the valve eventually overrides the spring. Eventually, (around 1200 pump rpm) that pressure differential causes the flow control valve to shift away from the discharge fitting causing a portion of the pump output to be recirculated back inside the pump. That is why it is called a flow control valve. This results in a nearly constant flow of oil out of the pump after about 1200 rpm. The rest is recirculated inside the pump.

 

thanks jim! it does more than i thought.