Ask the Expert – Play Detector Discussion

I was completing a demonstration with a customer today following the installation of his new testing bay.

This short blog post relates to those aspects associated with the design and the operation of play detectors used within One Person and Fully Automated testing bays.

The customer had concerns about the design of our GE457PD unit for class 4 and 7 testing because he anticipated that the side of the vehicle which had no unit underneath it would wear out his floor as the axle was loaded by the play detector situated on the opposite side.

Image of installation showing typical play detector arrangement.

To the contrary of this concern, the design of our unit actually minimises not only this risk of this but also the risk of damaging the vehicle.

This is because the GE457PD has been designed with the “non-driven” vehicle providing a force input control; that of the friction between the road surface and the tyre itself.

As the unit operates, the forces increase at the driven side until the limit of slip value on the play detector plate is exceeded – this means that the tyre begins to slip on the plate first rather than on the concrete floor.

Controlling the input force in this way does minimise/negate any damage to the concrete floor – but more importantly it negates the risk of damaging the vehicle with the test.

GE457PD’s are only suitable for pit based installations at this moment in time, GETECH however have other play detectors suitable for HGV, Bus & Coach applications as well as lift based versions to suit those using a lift rather than an inspection pit.

Single Vs. Dual & Pneumatic Vs Hydraulic

The conversation then moved onto if the single plate system or a two plate system was superior – as with most things in life there are pros and cons of both systems so its probably easier to describe here why GETECH products are designed as they are.

We prefer a single plate system for a number of reasons.

From a operational perspective you could design a 2 plate system with two rams in each plate or alternatively accommodate the entire system within a single plate which operates in all directions.

In opting for a single plate with 4 rams we gain other advantages. Firstly our groundwork costs are reduced by at least 50% as we only have to dig out one side of the installation to accept the plate. Secondly, as described above, we can protect the subject vehicle by ensuring the tyre slips on the play detector before the force is so high we damage steering or suspension elements in the subject vehicle.

As far as powering the operation is concerned one should also consider a hydraulic system to be superior. The forces always remains constant as we use a closed circuit to control the operation of the plate and we do not experience system losses as we might using air.  In addition, we do not need to add and water traps, compressors etc to our system (which would reduce reliability and would of course  increase costs).

GETECH Play Detectors are available to purchase online on our website [] with a play detector page being specifically located HERE.

getech-garage-equipment-logoGETECH supply MOT bays & equipment for all vehicle classes. As a manufacturer within the MOT scheme we are perfectly positioned to remain abridged of current and future known legislation. With a design ethos for total modularity, our equipment is some of the most flexible currently available in the UK.

For more information on GETECH call during office hours, visit or mail

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