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November 2018


Be safe with jacks

Be safe with jacks

Your guide to using lifting devices

Too many 'nasty accidents' when using jacks: CCA

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THERE are too many "nasty accidents" when jacks are being used to change wheels on caravans and camper-trailers, according to the Caravan Council of Australia.

"There have been reports of some jacks having their lifting mechanism unexpectedly failing, causing them to instantly collapse," founder and general manager Colin Young said.

He attribute the main causes as being jacks not being completely suitable for the particular caravan and not having their tops positively located to prevent horizontal sliding.

"It is essential that a caravan jack is appropriately approved and has a sufficient load rating and lifting range," Mr Young stressed.

He has now issued the following guide on the safe use of jacks.

Caravan jacks must:

• Be approved to the Australian Standard
• Have the top positively located - by a mating locating recess - to prevent any horizontal slippage
• Be operational for when the caravan is both empty and fully-loaded
• Be positioned on a firm base
• Have a sufficient load rating
• Have a sufficient length of travel

A caravan jack must:

• When on a firm base be low enough to engage a locating recess when any tyre is fully-deflated
• Have sufficient travel to enable a fully-inflated tyre to replace that tyre

Allowance must be made for the suspension "droop" when the caravan is raised.

Allowance must be made for the probability that the tyres(s) on one side of the caravan will be loaded greater than on the other side. Typically, this may be around 10 percent.

A conservative assumption must be made on the actual ball-loading. It is of course much more preferable to have had the ball-loading measured for the particular loading of the caravan.
While a typical caravan may have a ball-loading of around 10 percent of the actual mass of the loaded caravan, the actual ball-loading may only be around 5 percent.

The relationship between a jack’s load (lifting force) and its travel is a basic physics topic of moments… which is force multiplied by distance.

With the ball as the pivot, it is a "balance" or a "compromise" – for any given effective load (M) times its distance (LM) from the pivot – and the jack's available force (J) times its distance (LJ) from the pivot.

The jack's available travel (extended length minus retracted length) must be sufficient to enable a tyre to be safely replaced. M times LM equals J times LJ

The greater the LJ distance, the lesser the J force can be… and vice-versa.


Never rely on a jack … tragic accidents have occurred when a jack has failed or has slipped.

It is most important to practice changing a wheel/tyre before heading off on a trip so you know exactly what to do if you have the misfortune to have a punctured tyre on your travels.

• Do you know where everything you will need is stored… and how to use everything?
• Does the wheel brace fit the wheel nuts, and do you have the strength to loosen tightened nuts?
• Does the top of the jack correctly suit the jacking points on the underside of the chassis rails?
• Does the jack have sufficient lifting capacity (load rating)?
• Does the jack have sufficient travel … and is the minimum height low enough?

Always carefully read the warning notice and operating Instructions supplied with the jack.
If something is not clear to you, contact the manufacturer for clarification.

Typical (conservative) example:

All-up mass” of caravan: 2000 kg

Ball-loading: 100kg (5 percent of all-up mass)

Therefore effective load = 1900kg

Heavier side of caravan M: 1000kg

Lighter side of caravan: 900kg

LM = 2.00m

Therefore M x LM = 2000kg.m

Therefore J x LJ must equal (or exceed) 2000kg.m

If LJ is 3.0 m, J must exceed 667kg

If LJ is 4.0m, J must exceed 500kg

Typical Locating Device … positively locates the top of the jack to prevent it slipping in any horizontal direction.


 No part of this publication may be reproduced or transmitted without
the prior written permission of Dennis Amor.

Copyright 2005 Dennis Amor
All Rights Reserved

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