[Brian Considine]

Can someone experienced with hydralic plant settle an argument for me please ?

Discussing the incident on the M20 yesterday with a mate I said that (AFAIK) any hydralic plant being transported on a low loader should have the jib/arm/bucket restrained because if not, movement through one ram could cause another ram to expand, depending on how the plants controls had been set/left ?

Thanks in advance.

 

[levelrob]

The arm needs to be restrained to stop sideways movement to keep the arm (boom and dipper) and the attachment (bucket) within the width of the transporting vehicle.

The controls in the wheeled excavator in the incident are electric over hydraulic, so when switched off nothing will move. All hydraulic movements on the arm are by separate rams and hoses controlled by the controls in the cab through a dcv (directional control valve). The only movement you are likely to have when the machine is switched off is hydraulic creep (internal leaking past seals) or if a pipe bursts, but these days there are burst protection valves to stop any movement in this case.

In the incident (having just watched the BBC news pictures) it seems that the arm (dipper part, forearm) is vertical. This should be much lower either tucked under the machine or stretched out so that the highest part of the machine is a non moveable item i.e. The cab.

 

[Brian Considine]

Thanks Rob.

Is it posible that the arm is vertical because of the bridge strike ?

 

[levelrob]

Looking at the footage from the BBC no.

The bucket is on the low loader bed in a flat position, it looks like it was parked in that position otherwise it would now be sitting at an odd angle due to it being laid flat and then moved if the arm had moved in the collision.

It appears that the top of the dipper arm has struck the bridge and the force taken through the boom (upper arm) down to the machine its self.

If the arm was positioned all the way forward but too high the macine would have gone under the bridge and got stuck or ripped out the bridge but the bridge would have ended up on the excavator, if the arm was tucked underneath but too high then still the same contact point but the arm would still be tucked under.

There is what appears to be a site dumper infront of the bucket of the machine but then a gap up to the headboard of the truck trailer. Unless there was another item that has collided with the bridge that is not visible in the pictures on the BBC :*

With the site dumper in that position, (whoever loaded these machines) may have tried to lay the arm down but couldn't reach, then may have tried to fold the arm under the machine but with the bucket it wouldn't fit so just laid it flat and left the dipper vertical. Another option would have been to remove the bucket and strap that down as a separate item.

Without being there it's speculation but from experience being around plant for 30 years, hopefully no one was hurt which is the main thing.