-----Original Message-----
From: Al Gietzen [mailto:ALVentures@cox.net]
Sent: Monday, September 08, 2003 6:05 AM
To: 'Rotary motors in aircraft'
Subject: RE: [FlyRotary] Re: water flow restrictor

 

>

> Putting  flow restriction in an aircraft application where you want

> minimum radiator size and weight is a bad thing; in my opinion, of

> course.  The more flow the better - gives a lower temperature drop

> across the radiator, therefore higher average radiator for the same

temp

> going back to the engine.

>

> The idea of a flow restrictor is to provide higher pressure in the

> block, therefore increasing the boiling point somewhat; and provides

> back pressure to the pump which may reduce the risk of cavitation at

> very high rpm (like over 6000).  If you don't mind a larger radiator,

> OK.

>

> Size the radiator for about a 30F drop from inlet to outlet. Let the

> radiator provide the back pressure in the loop, maybe take advantage

of

> double pass.

>

> Al

 

Thanks for the advise, Al.  I understand about using the smallest rad

that will work, but that still doesn't address the issue of increased

boiling point (for micro bubbles I assume) or cavitatation.  Are these

an important issue???

 

These are important issues, but what are the gains?  Centrifugal pumps have a definite pressure limit.  The restrictor is going to gain you a few psi in the block with a penalty in the flow.  Higher flow also reduces the amount of nucleate boiling.

 

Use pressure caps to maintain higher system pressure; something we need at altitude anyway.  I'm using a 24# cap on the system, which is connected to the inlet side of the pump, with a 16 # cap on the overflow/expansion bottle.  The idea of the pressurized overflow bottle is to maintain pressure even when the coolant temp may be dropping when you reduce power.  I have a pressure sender at the pump outlet, and it will be interesting to see what that is at power – won’t surprise me to see 35 – 40 psi.

 

Al