Paging Doctor Lawryde

Yesterday I felt genuinely intelligent at work. I’ve kind of had to lay in the weeds and try to learn for the past six months. Most of the time people ask me a question about something I’d say, “I’m not really sure about that. I’ll have to look into it.”

The boom winch on a pipelayer was only operating the in the raise direction, and the hook winch was fine.

Where do you start trying to diagnose the problem?

Take some pressure measurements. Is the brake getting pressure to release? (For safety the brakes are on all the time and you need hydraulic pressure to release them). We had brake pressure. What are the raise and lower loop pressures during both a raise and lower command? Raise was normal as it should since it was working fine. Lower was hitting high pressure cutoff on the lower “A-side” of the counterbalance valve, and was getting absolutely no pressure on the raise “B-side of the counterbalance valve. (A counterbalance valve is a collection of valves in a casting that is on the motor that drives the winch, which allows for a smooth controlled lowering of a load. If you didn’t have it, when you lowered a several ton load it would just overrun the hydraulic system).

That was the big problem, high pressure on A and no pressure on B. This meant that somehow the oil wasn’t getting from the A side of the counterbalance valve through the motor giving up it’s energy and dropping in pressure to some level greater than zero on the B side.

I studied the hydraulic schematic for a while and figured it had to be one of the valves within the counterbalance valve was sticking and not allowing oil to go where it should. We took it apart, and one of the valves was kind of tough to move. It didn’t seem like it shouldn’t have been working, but we put it back together to give it a test.

It worked. It would raise and lower. I was exactly right about what was wrong. That must be what a doctor feels like when they correctly diagnose and treat a disease.

They finally posted the stats for our hockey league online. I have a link on the sidebar, but here they are:

We’re in second place. The first place team, which we’ve beat, is an offensive powerhouse with 48 goals for. We, on the other hand, are a defensive powerhouse with only 17 goals against and 14 penalties. Defense isn’t nice or pretty, old time hockey.