New gas compressor "takes off: Sertco applies aircraft, racing engine technology to gas compression packages

Diesel Progress North American Edition, Nov, 2003 by Norm Shade

When Sertco Industries Inc. decided to expand its business into gas compressors, it came with an unusual mix of innovation, talent and experience. Established in 1979, the Okemah, Okla., manufacturer has long been known in the highly competitive aerospace industry as a high-quality producer of precision structural airframe components for commercial and military aircraft.

This was not the first time that Sertco ventured into a new industry. In 1984, Sertco took the aerospace manufacturing process into the high-performance motorcycle racing world by forming its award-winning Motor Sports Division to supply high-performance parts to racers thruoughout the world. Among its accomplishments are big-block motorcycle cylinders capable of 500 hp for drag racing applications, a shock absorbing rear sprocket that has drastically reduced transmission breakage and a combination engine, transmission and clutch case that's capable of 50 percent more horsepower with reduced risk of catastrophic failure than original equipment.

The methods developed to support the aerospace and high-performance racing worlds led to the formation of the Energy Division in late 1998. Technology from the motorcycle engine project was deployed in the development of a reciprocating air and gas compressor. Starting development of its compressor line in 1998, the first Sertco compressor went into field testing the next year. By 2000, several units were operating at customer sites, allowing Sertco to monitor and improve its design under field conditions.

Sertco's initial entree into the market is its model 350 reciprocating compressor, a compact, eight-cylinder horizontally opposed unit that measures 29 in. long x 27 in. wide x 11 in. high and weighs 250 lb. Rated 30 to 125 hp at 800 to 2100 rpm for continuous duty, the compressor targets low pressure wellhead and vapor recovery applications that require a reliable, low-cost, high-performance solution. Allowable suction pressures range from 20 in. of Hg. vacuum to 25 psig with a maximum discharge of 125 psig. At these conditions the compressor is capable of flows ranging from 200 to 1200 mscfd.

Specifically developed for natural gas compression and vapor recovery, the engine utilizes stock GM 5700 industrial crankshafts, connecting rods and bearings in a precision cast aluminum alloy horizontally split block with five main bearings. The compressor crankshaft is balanced with steel counterweights and a harmonic balancer. The forged steel connecting rods are balanced and fitted with heat-treated AISI 8740 chrome-moly steal rod bolts. The Clevite tri-metal main bearings have low friction and high conformability.

Each bank has a four-cylinder head that is machined from an aircraft aluminum alloy billet. This material provides excellent corrosion resistance, high strength-to-weight ratio and rapid heat dissipation. The compressor cylinders are lined with centrifugally cast high-nickel iron alloy liners. The head design and valve placement allow for quick access to waives for inspection and service and discharge valve placement on the bottom reduces the risk of hydraulic lock-up. Hoerbiger 60RX series valves are used with all metallic plates to avoid the temperature limitations of plastic plates. Balanced, flat top cast aluminum pistons are fitted with Childs & Albert premium moly, "zero-gap" rings. The design permits a low clearance volume in the compressor, which started at a respectable 9.5 percent on the original prototype design and was improved to 3.6 percent with a new head and manifold design and use of heavier GM 366 pistons.

For corrosion resistance, hard anodized coatings are applied on all surfaces in contact with process gas and soft anodizing is used on other internal and external surfaces. SAE 304 stainless steel fasteners are used throughout the compressor. Cast-in cooling fins allow the compressor to be entirely air-cooled and the oil pump is mounted externally for ease of service. A separate oil pan is doweled and bolted to the crankcase.

"The Sertco 350 is the best compressor you've never seen," said Mikko Crouch, Sertco vice president. "Our initial sales were by word of mouth and we did no advertising until relatively recently, so our compressor is not well-known in the industry." That may be changing as the company reports more than 35 now in service and a growing order rate for new compressors. Crouch, who is just a little more than six years out of the University of Oklahoma with a business management degree preceded by a year in engineering at the University of Kansas, grew up with the Sertco business.

Sertco has all the tools needed to exploit the inventive genius of Mikko and his father, Richard Crouch, who founded the company and remains active as its president. With the ability to machine anything from aluminum to titanium, Sertco can handle projects from conception to final assembly or any portion in between. Eighteen CNC machining centers, with two-, three-and four-axis capability are organized in machine cells in a 21,000 sq.ft., environmentally controlled facility that features CAD/CAM and a full range of inspection equipment including two coordinate measuring machines. Supporting all major U.S. commercial and military aircraft manufacturers, Sertco has an excellent material tracking system, SPC data collection on every part after detailed first-piece qualification and a robust corrective action and preventative action program. A Boeing Silver Certificate for achieving a 99.5 percent delivery and quality rating is evidence of the company's manufacturing excellence. "Our quality system is certified to a level exceeding ISO 9002," said Richard Crouch.