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Test Rig for Water Softener Valves.

In normal use Domestic Water Softener Valves perform a complex sequence of water flow reversals though the brining chamber to regenerate and flush the water softener. This sequence normally takes an hour or two, and occurs only when a certain amount of water has been softened. The requirement was to perform a full test on every valve produced; but to only take a few minutes to perform test measurements at the five critical valve positions.

This system is designed to test the valves on the production line, after the mechanical assembly has been completed, but prior to fitting the valves own electronics and motor. Assembly is a complex process involving numerous small components and seals. The test rig comprises a fixture onto which the valve to be tested is clamped. This fixture has various water connections to the valve under test, which are made automatically. An large electric pump draws water from a collection tank and circulates it through the valve at up to 100 litres/minute and pressures of up to 2 Bar. Pressure and flow transducers measure the water pressures and flow rates passing through the valve and also measure the vacuum generated by a venturi suction section, which is built into the valve. The valves own turbine meter and photo-electric position sensor are also monitored by the test rig.

A 24vDC motor is mounted to the side of the fixture with an external gears to allow it engage with the plastic drive gear on the valve. The system is thus able to drive the valve under test to all itís operating positions and measure flow rates and pressures at each position. These measurements are compared with pre-set levels and a valve is only passed if it meets all the specified flows and pressures.

The control system comprises a dedicated real-time control computer, housed in a metal enclosure, on the front of which are various operator controls, together with function keys and an LCD screen and indicator LEDs. The screen is used to display the operating parameters and production data. The enclosure also houses the control computer and measurement interfaces. A separate enclosure houses the power supplies for the computer and transducers.

The system enables the various configuration and test definition parameters to be entered using a simple menu structure. This data is stored in battery-backed memory and is not lost if the system is powered down. The control computer used in the system is programmed in a high-level multi-tasking control language, which is an object-orientated real-time control language similar to PASCAL. The computer has opto-isolated interfaces to the various transducers and solenoid valves, and two RS232 serial links; one for the printer which produces Serial Number Labels, the other enables a portable computer to be periodically connected to download a Test History File and to record the Configuration Parameters.

Two systems have now been supplied. One has been in use in the UK for over a year, and has dramatically reduced the number of service visits required by field service engineers, as assembly faults are now trapped on the production line. The other has just been installed on a production line in China.