What If I Need To Choose A Chain Hoist Control System? - Part 1

What If I Need To Choose A Chain Hoist Control System? - Part 1

CX75 Staging What If

Part 1

So finally, we get to the topic of selecting a controller for your chain hoists.

The choice of controller features, both functional and safety related, largely depends on what you’re trying to do with your hoist(s), how many hoists you’re trying to control, and the risks inherent in what you’re trying to do.

In this article, we’ll look at the requirements for controllers when performing simple lifts with chain hoists – either a single point lift, or a 2 point lift with a horizontal (not tilted) straight truss.

In next month’s article we’ll look at complex multi point lifting, and discuss the pros and cons of synchronised hoists and networked controllers.

The correct selection of chain hoist will give you the first clues as to how simple or sophisticated the controller needs to be, as the various classifications of hoists under differing Standards or Codes of Practice mandate the minimum level of safety features that the controller must deal with.

Low compliance hoists, to BGV-D8 or BGVD8+ (Germany) or BS9706, Category B (UK) do not require limit switches or emergency stops.

High compliance hoists, to BGV-C1, BS9706 Category A and AS1418 (any application) all require both operating limits and ultimate limits, and emergency stops.

When operating a single hoist in either of these two groupings, a simple “pickle” controller will usually suffice, but you must bear in mind that high compliance hoists all require an emergency stop function.

If the controller does not have an emergency stop feature then you are effectively “de-rating” the high compliance hoist to a low compliance device - you cannot move a load over people’s heads without an emergency stop, regardless of the safety classification of the hoist doing the lifting.

The design of emergency stop circuits is covered quite thoroughly in AS4024.1604, but in a nutshell, an emergency stop must operate independently of the control circuit, and must either disconnect the power supply to the hoist(s) or use another approved method of safely disabling the hoist, such as a Certified “Safe-Off” control in electronic inverter controllers - simply adding a STOP button in the common conductor of the “Common/Up/Down” circuit of a control pickle does not qualify as an emergency stop feature.

We should also bear in mind that all high compliance hoists must be fitted with BOTH operating and ultimate “emergency” limit switches. The operating limits are required to prevent the hoist moving in one direction (e.g. the UP limit will stop the hoist moving up, but allow it to move down) and striking an operational limit is a normal hoist function.

The ultimate limits (both UP and DOWN) are there to immediately stop the hoist in the event that the operating limit fails to stop the hoist, and must cause an emergency stop to be initiated, so an emergency stop circuit is required to allow the ultimate limits to operate correctly.

Moving on from a single lift to something a little more complex, let’s say, 2 chain hoists lifting a truss, the same rule applies regarding emergency stops and limits, but now we must consider what happens if one hoist stops and the other hoist keeps moving, either from hitting a physical snag, striking a limit switch or from a fault on one of the hoists.

If you have qualified and experienced riggers performing this lift, then you can probably use 2 individual pickle controls or 2 channels of a basic multi channel controller and perform the lift quite safely.

If, however, there is a degree of “novice” involved with the operators, then serious consideration should be given to using a controller that stops both hoists when one of the hoists stops unexpectedly – this is known as a “group stop” and is the first feature we will examine next issue when we look at multi point lifts, synchronisation, position control and networking of hoists.

Read 'What If I Need To Choose A Chain Hoist Control System' Part 2 here.
Read 'What If I Need To Choose A Chain Hoist Control System' Part 3 here.
Read 'What If I Need To Choose A Chain Hoist Control System' Part 4 here.

 

Jands Staging provide articles to the "Staging What If" section in CX Magazine. If you have any questions regarding this article then please comment below or email info@jands.com.au

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