El Segundo, CA--By applying his unique positive-displacement pump technology to compressed air-foam (CAF) fire fighting equipment, inventor Eddie Paul has created a system that he believes will revolutionize the industry. Lighter and more efficient than competing centrifugal pump designs, it also offers a broader mixture ratio, significantly simpler operation, self priming capability, and lower power requirements.

CAFs work by mixing air with water and surfactant--basically soap--to create foam. The foam is a highly efficient fire-fighting fluid. It takes away heat and oxygen, acts as an insulator, requires a fraction of the water, and can last many hours before evaporating.

Paul's CAF system--known as CFX--is the first volume production application of the cylindrical energy module (CEM) positive-displacement pump technology he patented in the early '90s. It consists of six 1-inch diameter double-ended pistons that run in six bores equally spaced around a split, cylindrical cylinder block.

Each piston is fitted with a drive pin at its midpoint. The pins protrude through axial slots machined into the cylinder block and are fitted with rollers. A driveshaft is fitted to the cylinder block, and as it turns the rollers pass over a pair of matched sinusoidal cams formed into sleeves surrounding the block.

The cams drive the pistons through two one-inch strokes per revolution of the block. Since each piston is double headed, the CEM produces 24 strokes/revolution.

The pistons and liners are brass, and the head is bronze. Rugged, ultra-high molecular weight polyethylene forms the block and cams, while the rollers are Teflon-coated nylon.

Powered by a single-cylinder, 6.5-hp, 4-stroke engine, the basic CFX pumps 100 gpm at 1,000 rpm. Pumping efficiency is said to be greater than 90%. A larger unit, the Magnum, with a 1.5-inch bore and 1.5-inch stroke produces 300 gpm at 1,000 rpm.

The units draw in air and water through an intake opening fitted with a venturi. A single dial governs the ratio of water to air from 0% to 100%. The capability to run at such low water ratios is just one of the CFX's advantages over CAF designs, which can't operate with less than about 30% water.

Several fire fighting-equipment manufacturers market pumps based on their core centrifugal water pump technology developed for pumping water. Such pumps have inherent disadvantages compared to positive displacement pumps such as the CEM. In a centrifugal pump, pressure and flow vary in a non-linear fashion with respect to impeller speed, making it difficult to maintain a fixed proportion of water to air across a broad operating range. To address this characteristic, they incorporate complex proportioning systems that a trained operator must use to follow the pump "curve" that defines the nonlinear relationship.

In addition, centrifugal pumps can't pump air. Thus a compressed air source and regulator are needed. The CFX, by contrast, is itself an air compressor, making a compressed air source superfluous. Centrifugal pumps also have relatively low efficiency--less than 30%--requiring engines as powerful as 30 hp to drive them at 100 gpm.

Developing the CFX wasn't as simple as attaching a motor to an existing pump design. Paul optimized the materials and design for pumping the corrosive surfactant, and had to overcome several significant challenges along the way.

For example, early prototype pumps had a one-piece block that would cause the pump to seize when the block became warm and expanded. But if clearances were increased, the block wouldn't seal well against the head.

Paul's solution was to cut the block in half and put six springs between the halves. These not only maintain a constant seal against the head, they accommodate manufacturing tolerances, thermal expansion, and wear.

A second issue involved uneven wear across the face of the rollers. "They're basically in a continuous turn," says Paul, "and one side was skidding." The fix: bevel the cams and rollers so that each point across the rollers sees a constant speed.

His biggest challenge, however, has been getting a conservative, tradition-laden industry to consider a product--superior or not--from a new source. The easiest way to convert such skeptics, he's found, is to show them how well the CFX works. "We took a prototype to an event in Baltimore," says Paul, "and in eight seconds it put out a test fuel fire that had never even been put out before."

Additional details...Contact Eddie Paul, EP Industries, 150 Sierra St., El Segundo, CA 90245; (310) 322-8515