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Hand Lancing and The Law

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Length Of A Lance

reaction-force-barrel-length

 

Can I Use A Shorter Lance?

Before deciding to use shorter water jetting equipment, you need to ask yourself the following questions:

  • Could the work possibly be completed using a different technique?
  • Could the human operative be removed from the process? In other words, could the work be done by a machine rather than by a person?

If you have answered no to both of these questions, then you may use a shorter gun. However, as always, you will still need to stick to the safety guidelines laid out in the Blue Code of Practice.

Figures 1 & 2 will give you an idea of suitable flows and pressures to help you comply with the legal requirements.

 

speed-of-water-434

Generally, a pump that is being operated at 1000 bar pressure with the lance jetted to 34 litres per minute will exert 251 Newtons of reaction force.

As you can see in Fig 1, the water speed is 434 m/s.

speed-of-water-686

On the other hand, an ultra high-pressure pump which runs at 2500 bar and utilises 20 litres of water a minute will produce a lower rate of 233 Newtons.

Here in Fig 2, you can see that the speed of the water jet is 686 m/s, nearly one and a half times times faster than that shown in Fig 1. This means that this particular water jet will produce more of a cutting effect rather than blasting away chunks of the concrete.

40-litres-per-minute

If we joined two ultra high-pressure pumps together in one unit, the pressure would not double; however the flow of water would. This means that there would be 2500 bar pressure at 40 litres of water every minute.

Fig 3 shows us that the reaction force produced in this situation would be 467 Newtons.

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