1. Identification of switches. These physical checks and test procedures should be applied to models of "TAV Engineering" level switches that are prefixed with the following numbers: Type A: F150, F160, F171, 155, 156, 157, 170 (May 1987 - December 1996) Type B: B14-, B17-, F15-, F16-, S14-, S17- (December 1996 - 2006)
This prefix should be readily identifiable on the manufacturer's label fitted to the device e.g. F150 or F16-123-123 etc. If you have any doubts about the applicability of the 'checkable' switches fitted to vessels under your control, the switches may be identified by reference to the following descriptions of the check device:
Devices that are fitted with a small plate fixed to a shaft that is located within the main body of the switch assembly. The plate is able to pivot out of a slot in the body of the switch (the 'home' position) through an angle of approximately 90°. This enables it to be moved in the vertical plane and hence raise or lower the shaft. The plate has a hole drilled in its centre that will allow it to be locked or fixed to the main body of the switch when in the 'home' position.
Devices that are fitted with a pivoting lever that protrudes out of the side of the switch assembly and can be moved in the vertical plane. These levers may be fitted with a red sleeve. The levers have a pivot point located in a flange on the opposite side of the switch body. This flange also has a hole drilled in it that will allow the lever to be locked or fixed in a position where the lever is at 90° (perpendicular) to the main body of the switch.
If you are still unable to identify if your switch is affected, advice should be immediately sought from the manufacturer / supplier of the device.
2. Interim tests that should be undertaken.
It is important that all relevant switches have an interim test performed to ensure that they will activate the appropriate alarms, emergency shut down systems etc. in addition to ensuring that the check lever is correctly replaced and secured in the normal operating position.
To test that the switch is working correctly the lever / plate fitted to the head of the switch should unlocked or any fixing devices removed (should they be fitted) and then the lever / plate raised vertically to its highest position thereby simulating a high level in the tank (note - the plate operated mechanism will need to be rotated by approximately 90° to facilitate this). If the switch is working alarms and / or trip devices connected to the switch should operate.
In the event of any switch failing the above interim test procedure, appropriate steps should be taken by other means to secure the safety of the related tanks. This interim test does not negate the requirement for further, more thorough, proof testing and examinations of the alarm / trip system at the next practicable opportunity.
3. Returning the switch to the normal operating position. It is critical that after carrying out this test the lever or plate is put back into the correct operating position and is then padlocked or fixed firmly in place. Failure to do this can render the switch inoperative and hence overfill protection may be negated. With reference to the two switches noted previously the following procedure should be used:
Move the plate vertically until it is in a position level with the slot in the body of the switch assembly and then rotate the plate until it is fully seated within the slot. Following this action, secure the plate to the switch body by using a suitable padlock or fixing device  placed through the holes in the plate and main switch body.
Move the lever vertically so that it is at approximately 90° (perpendicular) to the main switch body. This will align a hole in the handle with the hole located in the plate adjacent to the lever's pivot point. Following this action, secure the lever in position by using a suitable padlock or fixing device 1,  placed through the previously aligned holes in the plate and lever. There should only be minimal free-play when moving the handle in the vertical plane.
 Any temporary padlock or fixing device installed whilst awaiting manufacturers equipment should only be removable with a key or tool.
 As an interim measure a 5mm diameter shackle / pin secured by a padlock or chain should hold the handle in the correct place whilst awaiting the manufacturers equipment