Indianapolis--It's a homeowner's nightmare: The shut-off valve in a dishwasher sticks open, allowing water to flow non-stop from the appliance, flooding the house, ruining the floors and carpeting.
Unlikely though it may seem, such accidents happen. Approximately four percent of all dishwasher malfunctions involve stuck valves, with the outcomes ranging from a slow drip leak to a flood.
By designing a special diaphragm insert for a new water shut-off valve, however, an engineer at Mallory Controls Division of Emerson Electric has dramatically reduced the likelihood of this turn of events. The insert--a plastic part measuring less than an inch in diameter--makes it much more difficult for water valves to stick in an open position.
It provides a simple solution that has eluded engineers for decades. Until now, the primary technique for preventing stuck valves has been to add filters, which screen out dirt and sand. By screening out particles, filters can eliminate the most common cause of stuck valves. But filters themselves can clog, thus defeating their own purpose. Other, more complex attempts at solving the problem have been unsuccessful, largely due to their cost.
In contrast, the plastic diaphragm insert succeeds because it is effective and inexpensive. Designed by Mallory Controls engineer James W. Richmond, the insert serves two main functions: It limits the quantity of dirt particles that pass through the valve's bleed port; and it dramatically reduces the possibility that stray particles will affect the valve's shut-off operation.
To achieve these results, Richmond limits the amount of water that flows through the valve's bleed port. Limiting the flow requires a delicate touch, because some water must flow through the bleed port to provide pilot pressure for the valve's operation. During operation, a small amount of water is channeled through the bleed port and into an upper chamber. Water pressure in that upper chamber helps to push the diaphragm down and shut the valve off when necessary. Richmond, however, believed that too much water flowed through the port, carrying sand, debris, and other particles that could compromise the valve's shut-off capabilities.
In order to limit the amount of water through the bleed port, Richmond designed the diaphragm with a tiny bump that butts up against a guide tube. When the valve is in the "on" position, water passes through a narrow channel inside the bump. The guide tube obstructs and slows its flow, but doesn't stop it.
Adding "vacuum break slots" to the device enabled Richmond to further slow the flow. The vacuum break slots, located at the base of the diaphragm insert, lower the pressure differential between the valve's upper and lower chambers. As a result, less water is drawn through the port and into the upper chamber. The ability to lessen that flow is critical, Richmond says, because the slower flow attracts fewer dirt particles. "You don't want to stop the flow through the bleed passage--that would affect the operation of the valve," Richmond says. "But you want to retard it, so that you don't have as many contaminants going through that area."
Invariably, however, some dirt particles do stream into the valve. And when they do, the new Anti-Clog design is far less likely to be affected by them. Richmond designed the diaphragm insert so that particles have little chance of getting caught between it and the valve's main flow passage. He accomplished this objective by making the body of the insert slimmer than past versions, and by incorporating a narrow rib on its outer diameter. The rib compensates for the slimmer body--with it, the insert has the same diameter as past versions. But the rib, in effect, leaves a very narrow strip of material on which particles can hang up.
The wider inserts left a broader area on which particles could get caught. In a worst case scenario, particles lodged between the body of the insert and the main flow passage, inhibiting the valve's shut-off operation.
To reduce the possibility of the bleed hole clogging, Richmond also provided it with a tapered opening. The tapered opening further reduces the possibility that particles will become lodged in a tight space.
Tapering the opening and adding the bump, rib, and vacuum break slots enables Mallory Controls to improve the valve's dirty-water life-cycle performance by at least 300%. During a seven-month test program, engineers verified the valve's life, flow rate, shut-off time, sound, and leakage--all without a single failure. The design received a Quality Achievement Award from a major North American appliance manufacturer, which now uses the component in its dishwashers. "It's been extremely successful at meeting our design objective," Richmond says.
Additional details...Contact James Richmond, Mallory Controls Div. of Emerson Electric Co., 2831 Waterfront Parkway, East Drive, Indianapolis, IN 46214, (317) 328-4000.