Sunday, December 30, 2012

Refrigerant Blending/Charging Cart

On my continuing quest to get repeatable results when charging the mixed refrigerants into my CryoBUG unit, I decided to put together a refrigerant charging cart (see below).

Blending/Charging Cart (click to enlarge)
This essentially combines 3 elements...
  1. Liquid Refrigerant Charging Glass
  2. High Precision Mirror Gauge
  3. Refrigerant Mixing Manifold
The charging glass is a modified version of a standard R-22 Charge-Check made by Thermal Engineering (see blog post: Creating an R-600a Charging Glass). This allows for precise measurement of the liquid part of the charge (in my case that would be R-600a).

The next part of the apparatus  required a precision method of measuring in the refrigerant gasses (R-23 or R-170, R-14, Argon). This was accomplished with a high accuracy pressure gauge (Marshal Town 0-400 psi 4.5" Mirror Gauge).

And to bring it all together, a refrigerant mixing manifold needed to be fabricated, which allows the individual refrigerant components to be metered into the CryoBUG unit without having to disconnect and reconnect charging hoses. This greatly simplifies the charging process, and minimizes any errors and/or contaminates from getting into the final mixture.

Charging Cart Diagram

Mixing Manifold and Pressure Gauge Assembly (click to enlarge)
I'm very happy with how the refrigerant mixing manifold turned out. Luckily for me I have access to a Bridgeport Mill, which made things so much easier when drilling out the brass block.

Afterwards, I installed five brass 1/8" NPT x 1/4" flare fittings to complete the assembly, and prepare it for refrigerant hose attachment.

For the base of the charging cart, I used one of those moving dollies that I picked up at Harbor Freight for about $17 (sale price). I then added a 3/4" piece of MDF to create a solid top, and a 4x4 post to allow for mounting the charging glass, pressure gauge, and mixing manifold.

Mixing Manifold and Gauge prior to Installation (click to enlarge)

After everything was mounted. I threw in a couple of short refrigerant hoses to connect the refrigerant gas cylinders and charging glass. Total cost on this project not including the gas cylinders was around $200.

Now I really think I am ready to resume my CryoBUG testing (yes, I know I keep saying this, but this time I mean it).


Anonymous said...

Looking good! Harbor Freight is always a great place to pick up odds and ends for a project like this.

CryoBug testing: Full speed ahead!

Michael St. Pierre said...

Thanks! Yeah I gave it it's first use yesterday, charged my CryoBUG Demo Unit, and it worked like a dream. Also got great test results, getting down to -148°C. It also confirmed what I had already suspected, that being that I was charging too much R-600a in my previous attempts when using a refrigerant scale. Judging by the compressor suction and discharge pressures, it looks like I should be able to tweak the Demo Unit to operate down into the -150's same as the prototype. something that I had thought not possible before.

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