Hydraulics in the cold

[joshuabardwell]

Says a friend of mine who works in dispatching/logistics: "I have 2 techs who, against advice, took their buckets up over 30ft and are now stuck because the hydraulic fluid is cold."

I thought y'all would get a chuckle out of that. Stay warm, everybody!

 

[oldnslo]

Sounds like a system design problem. Bucket lifts would be worthless to construction and lineman if they didn't work in cold weather.

 

[BeezFun]

I've never been stuck, but never understood why in cold weather the boom comes down so much slower than it goes up. The pump sounds like it's laboring more when I come down, which seems backwards. I guess I need to stare at the hydraulic circuit for awhile and see if I can understand it.

 

[joshuabardwell]

Sounds like a system design problem. Bucket lifts would be worthless to construction and lineman if they didn't work in cold weather.

I'm guessing that this is just far colder than they are designed for. The southeast is having a bit of a cold snap right now. Maybe they have a thicker blend of hydraulic fluid in them or something. I dunno.

I've never been stuck, but never understood why in cold weather the boom comes down so much slower than it goes up. The pump sounds like it's laboring more when I come down, which seems backwards. I guess I need to stare at the hydraulic circuit for awhile and see if I can understand it.

I'm guessing these are gravity descent.

 

[wdchyd]

I've never been stuck, but never understood why in cold weather the boom comes down so much slower than it goes up. The pump sounds like it's laboring more when I come down, which seems backwards. I guess I need to stare at the hydraulic circuit for awhile and see if I can understand it.

The counterbalance cartridge valves used in cylinder designs on bucket trucks are adjusted at higher pressures on descent......we see it all the time when bench testing in the machine shop with cylinders after a fresh rebuild

They adjust them higher to keep the cylinders from over-running the pump during cylinder retract and it gives added safety if a hose blows

It's not unusual to see 500 psi during extend cycle and near 2000 psi on retract

This might explain why the bucket lifts would not lower if the pumps/relief could not achieve the preset pressure on the counterbalance valves due to extreme cold

Bucket trucks (and cranes) up here see those cold conditions routinely and have heaters or low-vis oil to overcome the extreme cold

 

[wdchyd]

Also some cylinders have velocity fuse valves plumbed in......these tend to lock up prematurely when the oil gets too thick (cold)

Velocity fuses are basically hose break valves, they lock up when the velocity of the oil is too fast and they close like a check valve

 

[joshuabardwell]

A bit more info from the friend. The trucks are not dedicated bucket trucks, but custom box trucks with aerials on the top. Light-duty. Cold-weather capability was considered at purchase time, but was not deemed worth it, given how seldom we see extreme cold down here in the Southeast. There is apparently a safety release that will bring it down slowly, but that doesn't cause the boom to sit in its cradle so it can be secured, and without the boom secured, the truck can't be driven. So getting the worker down is just a matter of time, but driving the truck away requires a lot of "pouring hot water on it". The lulz continue.

 

[BeezFun]

The counterbalance cartridge valves used in cylinder designs on bucket trucks are adjusted at higher pressures on descent......we see it all the time when bench testing in the machine shop with cylinders after a fresh rebuild

They adjust them higher to keep the cylinders from over-running the pump during cylinder retract and it gives added safety if a hose blows

It's not unusual to see 500 psi during extend cycle and near 2000 psi on retract

This might explain why the bucket lifts would not lower if the pumps/relief could not achieve the preset pressure on the counterbalance valves due to extreme cold

Bucket trucks (and cranes) up here see those cold conditions routinely and have heaters or low-vis oil to overcome the extreme cold

That makes sense, but why does the pump/engine sound so much louder when I'm coming down than when I'm going up? It's a gas engine driving the pump, and I can hear/feel it labor more when boom comes down.

 

[wdchyd]

Cuz the pump needs to satisfy the pressure adjustment on the counterbalance valve before it can move the cylinder ........it works harder in the down circuit maybe even blowing over relief at the main relief when the oil is cold cuz of the high viscosity

 

[DeereMann]

Who'da thunk they need winter grade visosity hydraulic fluid in Tennessee?

Fabulous winter the eastern U.S. & CA are having. Meantime, western U.S. & AK are baking & bone-dry.