Hydraulics shines in touchless car wash

April 1, 2004
Automatic car-wash systems used to be built with engineering taking a back seat to price. But as car-wash owners realized the profit potential in higher quality and productivity, they began to demand more up-time, faster wash cycles, and cleaner cars.
A two-station Series D03 manifold controls hydraulics on the Super 5000 car wash.
The D&S 5000 is a high-pressure brushless car wash. A hydraulically controlled gantry passes over vehicles to automatically wash, rinse, and apply polishes and protectants.

That led car-wash manufacturer D&S Manufacturing Inc. to team with fluid-power distributor John Henry Foster Co. (JHF) and redesign the hydraulics controlling the wash-and-rinse process. The goal of these St. Louis-based companies, according to Dave Benedict, D&S CEO, was to use higher-quality components that would improve performance while holding the line on price.

The company's original D&S 5000 system featured a 7.5-hp motor driving a double pump (5.5 and 1.1 gpm). A three-station D03 manifold with standard directional valves controlled gantry motion and hydraulic motors on the side spinner and oscillator.

The wash cycle began when a vehicle rolled over a tire-treadle switch. The oscillators applied presoak as the gantry moved along the vehicle. The gantry would slow as it rounded a vehicle to wash the front and back while a hydraulic counterbalance valve prevented runaway motion. Subsequent steps included a high-pressure wash, rinse, and possibly applying polishes or protectants.

A review of the system identified several areas that needed improvement, says JHF's Ted Cassimatis. For instance, the unit ran hot and the gantry hydraulic motor would sometimes stall in extreme heat. A dedicated 1.1-gpm-gear pump fed oscillators that required only 0.6 gpm. And customers wanted to run the gantry faster without a larger motor.

For the redesign, JHF recommended a 7.5-hp electric motor powering a 6.5-gpm gear pump from Bosch Rexroth Corp., Industrial Hydraulics Div., Bethlehem, Pa. (www.boschrexroth-us.com), and a simpler two-station manifold to replace the three-station design.

A small custom block on the first manifold station houses a priority flow-control valve (0.6 gpm with ±25% tuning adjustment) for the oscillators, with the balance of flow routed to the main gantry. A Rexroth DO3 directional valve on the second station sends oil to the gantry, and a kick-down relief valve reduces pressure when the gantry approaches the end of stroke. This slows the gantry and eliminates the third station dedicated to low-speed actuation.

"The redesigned D&S 5000 was faster, simpler, higher quality, and more reliable," says Benedict, while lower assembly costs kept the system within the required price range. The success led to development of a new touchless car wash specifically for convenience stores and service stations. The D&S Super 5000 touts even faster and higher-quality washes, and can measure vehicles and adjust gantry travel distance accordingly. This gives a better wash on the rear of shorter cars and speeds cycle time. D&S can also vary speeds for each individual pass -- for instance, a slow wash and fast rinse.

Variable speeds and cycle times require ramping capabilities to give smooth acceleration and deceleration for the carriage and gantry movements, according to JHF. Given a high inertial nonoverrunning load and only one function operating at a time, JHF chose a Rexroth fixed-gear-pump system and proportional throttle valve for bleed-off speed control of the carriage and gantry. The proportional valve lets the Super 5000 run faster without abrupt starts and stops, and at variable speeds for presoak, wash, rinse, and optional extras.

"The Rexroth proportional throttle valve was really the key to the Super 5000 project," said Cassimatis. "It made the infinite number of speeds possible, while keeping the system simple with only one proportional valve to control both carriage and gantry functions. Car-wash owners can adjust each pass to their own preference with the ultimate in speed and flexibility."

A priority flow-control valve feeds other fixed-speed functions -- side spinners, oscillators, and optional side blasters. Each has manual independent speed control. This helps reduce cycle time by up to 30%, depending on vehicle size. A custom manifold incorporates all valving and reduces the number of piping connections, resulting in fewer leak points, easier access, and a smaller, lightweight package.

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