Military off-road trailers must be built to handle rough going, whether in rocky or sandy terrain, snow, or ice. To meet U.S. military specifications and safety requirements, their brake systems must hold for 24 hours once disconnected from a tow vehicle before an emergency parking brake is deployed. Yet, the brakes also must release dependably when needed. The solution is an air-piloted valve with tight tolerances and zero leakage.
Growler Mfg and Engineering, Star, N.C., builds trailers designed for two specific military tasks. The company’s A/M32K-10 munitions trailer transports air-launched weapons from a munitions storage site to the flight line at USMC expeditionary airfields. Its A/M32U-21 maintenance trailer provides complete power and air support for buildup operations of all munitions. The trailers incorporate an air-over-hydraulic braking system with an integrated surge system to accommodate multiple prime movers. The braking system includes an air pilot-operated valve that controls the pressure needed to actuate the hydraulic brakes.
Tight sealing in Doering’s piloted air valve allows it to meet military requirements to hold hydraulic pressure to 5,000 psi from a low-pressure pilot signal without leakage for at least 24 hrs while preventing cross-contamination of hydraulic oil and compressed air.
When the company decided to replace underperforming valves in these applications, it tested several and selected PAV Series air-piloted cartridge valves from Doering Inc., Clear Lake, Minn. The valves provide an interface between high-pressure hydraulic pilot signal up to 5,000 psi and a low-pressure pneumatic directional control to 150 psi. The valves come in a normally open or normally closed configuration with 2-way or 3-way operation and cracking pressure from 50 to 2,000 psi. They have an aluminum body (304 or 316 SS optional) with a stainless-steel wetted area to resist corrosion and are designed to prevent cross-contamination of fluids.
“We were looking for better control of the trailers’ air and inertia braking systems,” says John Crews, president of Growler. “The new valve needed to hold pressure tolerances reliably and stand up to off-road conditions.”
Two test criteria were switchovers and pressure requirements. Switchovers ensure that the valves change automatically to the appropriate braking system in accommodating several different types of tow vehicles in use at any time. During testing, the new valves successfully switched over and back 100 times without failure within the time requirements. The valves also performed well against target pressure ranges, switching reliably at 20-30 psi. In contrast, the previous valves would switch at anywhere between 30 and 80 psi.
“The PAV valve is better designed and manufactured,” Crews said. “It doesn’t allow the air and brake fluid of the two systems to interface. These valves hold to the strict tolerance our customers need for safety and reliable functionality.”