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).

Thursday, December 13, 2012

Creating an R-600a Charging Glass

Charge-Check Model #7003
I got my Ebay purchase a couple of weeks ago, thinking that I was getting a Charge-Check 7001 (16 ounce) charging glass, but instead I ended up with the 7003 model which holds 2-1/2 lbs (40 ounces). Although for $25 I couldn't complain too much.

However this was quite a bit more volume than I needed, and my concern was that the resolution was going to be very poor as a result of this. With my CryoBUG unit requiring less than 50 grams of R-600a, I knew that it would be very difficult to measure this out accurately. It seemed like my best option would be to displace some of that extra volume by the use of an internal displacement device. So the first order of business was to disassemble the Charge-Check.

7003GS Gasket Set
Very quickly after pulling things apart, I realized that the seals were not reusable. After Googling around for a bit, I came across a gasket set being sold by a company called FieryChill for $33. After adding in shipping for both items, I was now up to $78. Still not bad considering that a brand new Charge-Check would have cost me around $178-$200.

So while I waited for the gasket set to arrive, I went about creating a suitable displacement vessel to mount inside the original Charge-Check cylinder. I had some 1-5/8" caps and tubing left over from an earlier autocascade project (used for making refrigerant liquid/vapor phase separators). And this seemed to give me the ratio of open v.s. closed area that I was looking for.

I cut the 1-5/8" tubing to fit inside with a small amount of vertical space to spare. Next I silver soldered a small threaded stud to the bottom of one of the caps, after which I brazed the caps to the tubing. The stud would be used to secure this displacement vessel to the bottom end cap of the Charge-Check, after a hole was drilled and tapped to fit the stud.

I then bead blasted the original cylinder to remove the R-22 measurement sticker, gave it a coat of paint, and reassembled the Charge-Check with the newly made displacement vessel inside.

After insuring that everything was leak tight, I filled the Charge-Check with two 5.5 ounce cans of the Wall Lenk iso-butane fuel, having previously measured the empty weight of the Charge-Check with my electronic scale.

Subtracting the filled weight from the empty weight, yielded the actual net weight of the iso-butane now residing in the Charge-Check. This ended up being fairly close to what was suppose to be contained in the Wall Lenk butane fuel canisters that I used.  Final weight was 10.5 ounces. With a liquid column height of 13 inches this converted to 1 ounce for every 1.25 inches of height. Using DeltaCad, I created a new measuring scale based on this information.

Here is a look at the finished R-600a Charge-Check produced by all the modifications (click on the image to enlarge). I got the measuring scale printed on card stock and laminated at my local Kinko's. This ended up adding another $5, bringing the total price of my customized Charge-Check to $83.

As can be seen, I also included a kilogram scale as well, having increment marks spaced at 10 grams each.

Now I just need to get back to my original project, that being charging, testing, and tuning of my latest CryoBUG Demo unit.