leitmotif said:
1. What kind of diagnostics will you do based on swash plate angle?
2. How well or not well my bright idea works out and why or why not.
This is an application where 11 large diamter pistons are rapidly extended, then force is applied against a load that achieves static conditions at 5500 PSI, the pistons stop moving and pressure is maintained via servo valve to continously apply force.
We configure our pumps with dual high pressure/low flow and low pressure/high flow controls, lately we have been using electronic variable pressure and variable displacement controls on the pump. This lets us move the actuators very fast with high flow and low pressusre and then switch to high pressure low flow controls for force application. There are several advantages to that, one is that you can keep your motor size down and still use only one motor/pump. We also employ horspower limiting controls along with the pressue and displacement controls on the pump, which IMO is a good idea with high/low controls to keep the pump from being fully on stroke at high pressure and over amping the motor.
Once static pressurized conditions are achieved, one quick way to check and make sure that we don't have any internal leaks in any actuators is to look at the pump swash plate angle. If there is still displacement then fluid must be going somewhere. With the high flow/low pressure low flow/high pressure pump control arrangmenet its possible for internal leaks to go undetected for a long time because the pump has the ability to move more than enough volume to overcome significant leaks simply by brute strength - but with a penalty in increased load on the motor - as long as the leak is not so large that we reach the horsepower limit then the leak can go undetected. We can tolerate and overcome a leak in any one of the eleven pistons, but not two. Unscheduled downtime on these machines really hurts production in ways that virtually cripple the entire plant. The large diameter pistons take a long time to rebuild so we want to detect problems and schedule for maintenance instead of being caught by surprise as a bad time.
Right now we have operators and maintenance montitor the pump swash plate angle as part of regular PM checks however it is inconvenient, and as ya'll know, inconvenient checks don't always get done like they should be. The motor load data from the smart soft starter is available on diagnositcs screens available to the maintenance techs but not the operators. We also haven't trained our operators on what motor load means and some of our maintenance guys don't understand it but they get that if there is flow after the ring is closed there is a leak - so I have never emphasized it - and until your post it just didn't cross my mind that I could maybe develop a visual tool on the HMI to use motor load data to convey the information that someone may want to get out the ultrasonic ear and go listening for a leak or start looking for hot lines on the pistons. All I will need is some logic that indicates that the ring has closed and we are static and then an indicator that indicates if motor load is above the expected values at that state.
Bud is spot on, there are multiple flow/pressure solutions for a given motor load, but actual flow volume isn't what I needed anyway, just whether there is any flow or not. Since there is a pressure transducer I could use that in conjunction with motor load but I don't think It'll be necessary - I'm inaginaing a basic needle gage on the HMI with a green zone and a red zone and a warning message in the alarm banner. I'll have to empirically determine green/red conditions but that won't take long. Besides, we painted green and red lines on the pump above the swash plate angle indicator for the operators, this will be virtually the same. I don't know why I didn't think of it. Thanks again guys for the input and brain storming.
