It's Megan from the content team at Lifco, we're talking to Fraser and asking some in-depth question regarding a recent video. In this video we had an older pump a Linde BPV 50 come in off of an tractor. The customer asked if we could repair this as economically as possible. Read our conversation below where we discuss this pump and what we did to get it working properly again.
Video: Linde BPV50 Troubleshooting
Megan: To keep the costs low can you explain what we did differently than what we would normally do for a regular troubleshooting?
Fraser: A BPV50 is a closed loop pump, which means it has two ports, A and B, and they connect directly to the A and B port of a hydraulic motor. The connection length is kept as short as possible and it is uninterrupted (ie. no filters or a reservoir). The result is: whatever bad happens to the pump or motor first will probably very soon damage the other. So the first shortcut we took was that we only looked at the pump, not the motor.
The second way we were able to reduce the cost was to reuse parts that we typically would say need to be replaced. It won't last very long and it won't be as powerful, but it will work. However we need to be careful that we don't get greedy: if we put something that doesn't work at all or even worse, like a bearing that breaks, this whole job could be a waste. I think we found the right balance based on our experience. We have about 30 years of experience with this unit.
Megan: So because we only worked on the pump, the issues they were having will most likely still happen until the motor is also looked at?
Fraser: The pump was really worn out and the controls did not work. It did not look like it was damaged by something like a contaminate. There is a chance that the motor is worn out and non-functioning. Lots of uncertainty and the owner just needs to weigh the risks.
We have seen this a few times. Often it is "just make it run onto the auction block".
Megan: Okay yeah, that makes sense. I mean we tested the pump on our bench and it seemed to be working well, there's a chance we just gave the pump a little more life. You guys talked about the "inching valve" a lot. Is that what the control is on the pump?
Fraser: There were a couple of controls but the "inching" function was malfunctioning. That BPV50 had an electric non-proportional on/off control (all on or all off, like a standard light switch). Then it had the inching function that "dims" the pump when it is ready to either move slow, or operate other hydraulic equipment on the machine. For instance if they are driving fast somewhere, and then they still want to be able to drive slow and lift something or operate a street sweeper. The operator turns the lever and reduces the amount of torque to the pump. Actually remarkably similar to that triple Rexroth that was in our shop (the one with the input shaft that was missing its splines). Its a little fancy, and not very common.
Megan: Do they still make pumps with that function?
Fraser: They do. The Linde "CA" control is the current one. But super rare. Most equipment now has electronic controls that do everything it needs. Remember, all these controls do is move a swashplate to produce more flow or less.
Megan: Okay, interesting. Do we maybe have a schematic we can share of it ?
Fraser: (Schematics shared below. See diagrams 1 and 2)
Megan: These pictures make me feel like saying the inching valve is only a very small piece in the whole system.
Fraser: The Y and Z are those on/off switches
Megan: On and off as in the lever that Lloyd was twisting on the pump when it was on the bench? Or is that something different
Fraser: No he was twisting the inching valve lever (see in the schematic that it protrudes outside of the lines). If you energize the coils on Y or Z then it pushes the spool against the spring and the oil flows from bottom left to top right (right now it is in neutral position because the spring is connecting bottom right to top right).
If you could accurately describe what is happening with that inching valve function then it's likely you are an engineer at a pump manufacturer. It is a very difficult one to get started with, but hey: we take the material as it comes.
Megan: Yeah ill be honest I was really confused looking at the schematic but I at least understand the basics of what you described the inching valve does. It's an interesting one for sure.