Oil-less compressor eases refrigerant recovery

Sheboygan, WI--When lawmakers mandated recovery of all system refrigerants in 1992, the legislation seemed the perfect deterrent to the undesirable effects of chemicals on the earth's atmosphere. Unfortunately, recovering refrigerants involves a whole new class of engineering challenges.

Certain refrigerants are incompatible with the compressor oils used in some recovery systems. As a result, refrigerant removal services must own several types of recovery systems so they can correctly match compressor oil to refrigerant.

Now, however, a new oil-less compressor design solves that problem. Designed by Thomas Industries specifically for refrigerant recovery systems, the new compressor can be matched with any type of refrigerant. As a result, users only need to purchase one recovery system.

Until now, commercially made oil-less recovery systems had normal single-stage compression ratios (approximately 20:1). But refrigerant recovery systems need higher compression ratios to pull the air conditioning system down to required vacuum levels--particularly when the system's receiving tank is at high pressures.

Thomas engineers solved that problem by designing a compressor with a high volume ratio. To do so, they minimized clearance volume within the compressor's cylinder. That step proved critical, they say, because additional clearances lower the volume ratio and, in turn, diminish the compression ratio. Sources of additional clearances include cylinder head recesses, seemingly innocent O-ring grooves, and extra volumes required for such items as screw-head drive sockets. The new compressor, which has a swept volume of 0.361 cubic inch, features a clearance volume of just 0.006 cubic inch.

Key to maintaining a low clearance volume is a fastenerless design for the compressor's inlet and discharge valves. The new design departs from previous reed valves in that it eliminates the need for a screw to hold it in place. Instead of a screw, Thomas' 515 Series Air Compressor uses a temporary adhesive to mount the reed valve in place during assembly. The valve fits into a recess only slightly deeper than the valve itself. After compressor assembly, the inherent geometry of the valve plate and cylinder lock the reed valve in place.

The valve design provides engineers with a dramatic advantage in terms of the cylinder's clearance volume. By using a fastenerless design, they eliminate the need to add a special recess to accommodate a screw head. Such a recess would increase the clearance volume, possibly doubling it. As a result, the volume ratio and compression ratio would drop.

But by employing the fastenerless valve, engineers can maintain a low clearance volume and a much higher compression ratio. The 515 features a compression ratio of 60:1, an extraordinarily high figure for a single-stage design. "We're able to pull much deeper vacuums at high receiver pressures with this ratio," notes Shawn Leu, project engineer for the 515 Series compressor. Leu adds that conventional compressors capable of achieving the same ratios typically do so with large two-stage designs, a luxury that's not cost effective for compressors used in refrigerant recovery systems.

Specially designed O-rings made from epichlorohydrin (ECO) also played a key role in the success of the new compressor. The ECO O-rings enabled engineers to meet stringent requirements for compatibility with multiple refrigerants.

The combination of technologies used on the new compressor reportedly provides twice the life expectancy of competitive units. Customers benefit because they now need to purchase only one recovery unit instead of two, and because the one they purchase will last longer.

"If you wanted an oil-less compressor for these applications in the past, you had to build your own," says Jim Gartman, OEM product manager for Thomas. "We knew that if we could build a compressor specific to the application, it would solve a lot of problems. And it has."

Additional details...Contact Jim Gartman, Thomas Industries, 1419 Illinois Ave., Box 29, Sheboygan, WI 53082, (414) 457-4891.