X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from email2k3.itlnet.net ([64.19.112.12] verified) by logan.com (CommuniGate Pro SMTP 5.0.3) with ESMTP id 872041 for flyrotary@lancaironline.net; Sun, 11 Dec 2005 23:52:37 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.19.112.12; envelope-from=jwvoto@itlnet.net Received: from rav.itlnet.net (unverified [192.168.10.149]) by itlnet.net (Rockliffe SMTPRA 6.1.20) with SMTP id for ; Sun, 11 Dec 2005 22:51:51 -0600 Received: from JWVOTO (unverified [64.19.115.106]) by itlnet.net (Rockliffe SMTPRA 6.1.20) with ESMTP id for ; Sun, 11 Dec 2005 22:51:49 -0600 Message-ID: <002e01c5fed8$c778c920$0100007f@JWVOTO> From: "Wendell Voto" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Radiator Expansion Tank Date: Sat, 10 Dec 2005 22:18:15 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0156_01C5FDD7.9E7FD1A0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4133.2400 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400 This is a multi-part message in MIME format. ------=_NextPart_000_0156_01C5FDD7.9E7FD1A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Subject: [FlyRotary] Re: Radiator Expansion Tank Thanks Al. Wendell Al, Rusty and others. I've been a little confused with the set- up recommended. Do you have = a pressure cap on the Radiator as well as the Expansion tank and do you = have an overflow bottle attached to the expansion tank. I've also seen where the rad pressure cap is not on the rad but on the = return to the pump. I would really like to sort this out so that I get a clearer picture = of the correct set-up. Advice appreciated. George ( down under) George; My system has two pressure caps. The filler neck on the left in the = photo connects to the pump inlet side of the loop (lowest pressure = point). That neck has a 23 # cap; and when the system is full and = purged, there is never any air at that cap. Overflow from the main = filler is plumbed to the bottom of the overflow bottle. The overflow = bottle normally is maybe half to two-thirds air as required to = accommodate the expansion from cold to hot. It has a 15# cap. =20 The idea is to always have positive pressure on the inlet side of the = pump to inhibit cavitation. Without a pressure cap on the overflow = bottle, expansion of the coolant in the engine pressurizes the system as = it heats up. But with no air in the system, after the peak is reached, = the pressure goes back to zero (or slightly negative to draw coolant = back from the overflow bottle) any time the temperature drops a bit; as = when you reduce power after climb-out. There are no caps on the radiators (2) as they are mounted at lower = levels. There are air bleed lines from the highest point of the tank on = each rad that go back to the filler neck; which is always at the lowest = pressure in the loop so the air will go there. With both caps fully latched, it is possible for the pressure to peak = at about 38 psi (23 plus 15), at sea level, if the overflow bottle is = full (coolant fully expanded). This give more margin (higher boiling = temp) and less likely cavitation at extreme conditions. Generally there = is always residual air in the bottle that is compressing, so the = pressure doesn't reach peak. Caps are 'differential pressure' so at = higher altitude the absolute pressure in the system is lower. A similar, and simpler approach is to have an expansion tank that has = air in it connected directly to the system, say as a filler tank with a = pressure cap, that is only half full when cold. Pressure builds as = things heat up, up to the max cap pressure. The difference in my = approach is that the pressure builds very quickly to the system cap = pressure because the coolant is incompressible (not counting some = expansion of hose connectors). So even if the engine is not fully = warmed up and I give it full throttle on takeoff, the system is at least = 23 psi at the pump inlet. Same is true any time later when power (and = RPM) is increased. Hope this all makes sense, Al -------------------------------------------------------------------------= ----- -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net/lists/flyrotary/ ------=_NextPart_000_0156_01C5FDD7.9E7FD1A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
Subject: [FlyRotary] Re: = Radiator=20 Expansion Tank
Thanks Al.
Wendell

Al, Rusty = and=20 others.

 

I've=20 been a little confused with the set- up recommended. Do you have = a=20 pressure cap on the Radiator as well as the Expansion tank and do you = have an=20 overflow bottle attached to the expansion = tank.

I've=20 also seen where the rad pressure cap is not on the rad but on the = return=20 to the pump.

 

I=20 would really like to sort this out so that I get a clearer = picture=20 of the correct set-up.

 

Advice=20 appreciated.

 

George=20 ( down under)

 

George;

 

My = system has two=20 pressure caps.  The filler neck on the left in the photo connects = to the=20 pump inlet side of the loop (lowest pressure point).  That neck = has a 23=20 # cap; and when the system is full and purged, there is never any air = at that=20 cap.  Overflow from the main filler is plumbed to the bottom of = the=20 overflow bottle.  The overflow bottle normally is maybe=20 half to=20 two-thirds = air as=20 required to accommodate the expansion from cold to hot.  It has a = 15#=20 cap. 

 

The idea = is to=20 always have positive pressure on the inlet side of the pump to inhibit = cavitation.  Without a pressure cap on the overflow bottle, = expansion of=20 the coolant in the engine pressurizes the system as it heats up. But = with no=20 air in the system, after the peak is reached, the pressure goes back = to zero=20 (or slightly negative to draw coolant back from the overflow bottle) = any time=20 the temperature drops a bit; as when you reduce power after=20 climb-out.

 

There = are no caps=20 on the radiators (2) as they are mounted at lower levels.  There = are air=20 bleed lines from the highest point of the tank on each rad that go = back to the=20 filler neck; which is always at the lowest pressure in the loop so the = air=20 will go there.

 

With = both caps=20 fully latched, it is possible for the pressure to peak at about 38 psi = (23=20 plus 15), at sea level, if the overflow bottle is full (coolant fully=20 expanded).  This give more margin (higher boiling temp) and less = likely=20 cavitation at extreme conditions. Generally there is always residual = air in=20 the bottle that is compressing, so the pressure doesn’t reach = peak.  Caps=20 are ‘differential pressure’ so at higher altitude the = absolute pressure in the=20 system is lower.

 

A = similar, and=20 simpler approach is to have an expansion tank that has air in it = connected=20 directly to the system, say as a filler tank with a pressure cap, that = is only=20 half full when cold.  Pressure builds as things heat up, up to = the max=20 cap pressure.  The difference in my approach is that the pressure = builds=20 very quickly to the system cap pressure because the coolant is = incompressible=20 (not counting some expansion of hose connectors).  So even if the = engine=20 is not fully warmed up and I give it full throttle on takeoff, the = system is=20 at least 23 psi at the pump inlet.  Same is true any time later = when=20 power (and RPM) is increased.

 

Hope = this all=20 makes sense,

 

Al

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Homepage:  http://www.flyrotary.com/
Archive and=20 UnSub:  =20 http://mail.lancaironline.net/lists/flyrotary/
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