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Jeff,
In my system, the outlet of the water pump (high pressure and coolant high level) is connected to the expansion tank at a location a couple of inches from the bottom of the tank. The inlet of the water pump (low pressure and low coolant level) is connected
to the bottom of the expansion tank. Both connections to the coolant tank are below the coolant level in the tank at all times. With the engine not running, the expansion tank does not back-fill with coolant even if the expansion tank filler cap is removed.
In my system, the expansion tank cannot back-fill unless the volume of the coolant in the rest of the system is increased (by thermal expansion for example) or air is introduced into that part of the system.
Steve
From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of Jeff Whaley <flyrotary@lancaironline.net>
Sent: Thursday, January 29, 2015 11:50 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: swirl / expansion tank configuration
Steve, nothing wrong with connecting both hoses to bottom of expansion tank as you indicate; however, it’s the connection points to the engine block that are important here. If the other end of one hose is connected to a low-point in the
system the expansion tank will back-fill with coolant - that is in the static condition: engine not running, pressure cap on expansion tank removed and system not pressurized. One connection should remove steam from block; the other connection goes to top
of water pump not the bottom. That is how my system is connected and I think yours is too. System pressurizes in relationship to coolant temperature; I use a 16 lb cap on my expansion tank (not lowest point either) typical cruising pressure will be 8-12
psi.
Jeff
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