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From: Roger L. (no email)
Date: Fri Nov 04 2005 - 10:18:34 EST
Hmmm....As a engineer I've dealt with exactly this problem a lot in the past 15 years. I've tried to shift bubbles in industrial pipelines using every trick I can think of including high flow rates for long periods of time. I can tell you that if you have a section that has a bubble, then very probably that bubble will be staying there until some combination of pitching and rolling allows gravity/buoyancy to move it.
Just flowing fluid past the bubble is unlikely to move it. I have watched the photos of bubble vs fluid flow through special clear sections inserted into high pressure/high flow water lines. It is amazing how a bubble occupying more than 3/4 of the area of the pipe will flex and allow water to speed up to flow under the bubble without ever threatening to flush it through.
Sometimes the bubble does get flushed through, but even so as long as the high spot in the pipe is there then outgassing from the fluid renews the bubble in a remarkably short time. Often only a few minutes.
There is some good news here. One is that the new bubble is only partly air. It is mostly a vapor form of whatever fluid is in the pipe and so has at least some of the characteristics of the liquid around it.
The second bit of good news is that if you can raise the pressure & flow rate from the pump, then you will find that the bubble itself does not restrict the flow rate nearly as much other obstructions in the line such as valves, kinks, or even bends in the tubing.
I think that the answer to your question is to prime it as well as you can using any method. More importantly, you must have some sort of valve to release trapped air from the highest place in the system. Several places are better than one. And accept that the remaining air will both be larger than you think, and have less of an effect on the system than you feared.
Roger L. F28cc
----- Original Message -----
From: Sea Quell crew.
To: ;
Sent: Thursday, November 03, 2005 6:50 PM
Subject: [CASCADIA] Bleeding and priming hydronic heater.
What's the most effective and convenient way to prime 100 foot of hose
that is routed through the boat?
I have a Webasto hydronic heater, so the heating fluid is pumped through
the boat via 3/4 inch hose.. I recently replaced a hose that had a kink
in it that was restricting flow. Now I have some air in the hoses. I
suspect there is air trapped at the pump area. So the pump is not
moving the fluid. There are no nozzles to bleed air near the pump.
This hose obviously is not level, it goes through cabinets, so there are
low and high levels throughout the boat.. Towards the end of the hose
loop is an expansion tank that does allow air to bubble out of the
system. Also, some of the heater registers (fan units) do have bleeding
nozzles.
Any suggestions?
Thanks,
-Neal.
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