Gentlemen ,

Can I get a good solution to find hydraulic oil leakages in Hydraulic lines , and once leakage is confirmed ,Our system PLC will switch off the electric motors. I have already tried Hose Break valves , The results were poor .

thanks

david

Can you explain the system more?

We use a 0-2 psi pressure transducer to monitor tank level and have a rate of change over time to monitor for leaks(all of this is interfaced with a PLC)-not sure if that is what you are looking for.
Maytag

The system is for a Tyre Vulcanizer - Hydraulic type . We have this power pack common for operating 5 Presses . The tank is non Atmospheric vented type . The oil level fluctuates to a differences upto 200 mm with an overall oil level of 750 mm in the reservoir , depending of press oil consumption. We have installed a oil level sensor , which can sense Over filling Warning , Low level alarm , Low level system cut off . The overall Hydraulic system have 14 cylinders / press . with a running line of 140 meters /press .

Maytag ,

Could you please explain your logic with 0-2 psi PT ? My tank is of non pressurized type .

thanks ,

david

maybe your systems hydraulic fluid is above mormal level.

We use a transducer made by Pressure Systems Inc. I'm in a steel mill-most of our applications are water/glycol(all are vented also)-if my memory serves me correctly 50 inches of W/G is approx 2 psi-this FULL level is of course 100%. When the level drops to 90% and holds that lower level for a sustained time we get a low level indication. I'm a mechanic and did the math for the full level and did all the installations but my electrician did the program and he is no longer with this company.
Some of the programs have been tweaked a ittle to compensate for level changes when extending cylinders with a larger area ratio (blind end to cap end). Our systems are not solely dependant on these PT-we use a float switch assembly for a back-up.
Maytag

If you know the oil level with all presses shutdown, and you can calculate the volume of oil used by all of the presses and accumulators, you can establish a setpoint the PLC will use to shutdown the presses. (You could also record the oil level, start all presses and manually put them in the condition where oil use is highest, then record the final level.) For example - if the "shutdown" oil level is 900 mm - and the maximum usage in level is 200 mm, have the PLC warn of a leak at 690mm, and shutdown at 650mm. With a level sensor, the PLC can read the "shutdown" oil level (since levels can and will change somewhat) and do the math for you. If you want to get really technical - add rungs that monitor which presses are running, and adjust the "delta" oil level based on that. It's not an exact method, as most presses won't be in the cycle to give you the maximum level change, plus charged accumulators may still loose oil - but it's a starting point. (There are several highly accurate level sensor types, including ultrasonic and magnetorestrictive that can provide continous oil level monitoring.)

If!!!!! the pump system has a dead time, no flow required since all the presses are completely open or closed and stopped, you could use a 0-5 GPM Flow Meter with electric output to send a signal to the PLC that there is flow when no press requires flow.

Out of the pump use a Tee with the straight through connected to a 35 PSI Check Valve free flow to the circut. Connect the outlet of the Check Valve to another Tee with its straight through outlet going to the press circuit.

On the branch port of the first Tee's plumb the 0-5 GPM flow meter at the Check Valve Inlet side and the flow meter outlet into the second Tee branch port. This allows flow through the flow meter up to 5 gpm and all other flow to the circuit. An orifice before the flow meter wold keep it from seeing excessive flow and prolong its life and accuracy.

This setup would send any low circuit bypass flow to the flow meter which could signal there is a leak or bypass.

Gentlemen ,

Adding a flow meter as suggested by Bud looks to be a possible solution , which I can work for . I am exploring the possibilities for implementing the same .


David

David;

Replacing the Tee's with 3-Way Ball Valves would be another/better way to install the flow meter. that way the flow meter would only be used to Trouble Shoot a suspected bypass problem. I put a Bleed Circuit to drop all pressure on the Flow Meter installation after it is used.

If you have Isolation Valves at each Press it would be easy to isolate and Trouble Shoot which circuit had the bypass. Simply open the Flow Meter circuit and open each isolated press circuit individually.

I always offer an option on any circuit I design for Flow Meters, Isolation Valves and Gauge Test Ports that allow for fast and easy Trouble Shooting. It cost's more up front but usually cost's less than the production loss from the first downtime due to a hydraulic circuit problem.

Bud ,

Our press system needs an online monitoring for leakages , always . So adding a check valve system as suggested by you may fit better in this case .
In case of Ball valves , A maintenance technician have to go physically shift the ball valve for finding the leakage .

My plan now is install the flow meter with a check valve bypass circuit , If the flow meter senses beyond 2 lpm while no press operations . It will give an alarm with a siren to inform the plant operator . Further the operator can take a call to switch off the power pack or to continue .

david

quote:

We have installed a oil level sensor , which can sense Over filling Warning , Low level alarm , Low level system cut off .

David, is that an analog oil level sensor with an analog output and PLC programmed alarm points, or is it a sensor with a series of switches?

If you have an analog output to the PLC then you already have all the instrumentation you need and don't need the flow switch. Monitor the rate of change of the tank fluid. If its changing when it shouldn't be, or its changing faster than it should be, then you have a line break.

You can also use it to limit the re-fill level of the reservoir even with the presses in operation, if pistons are advanced then subtract the appropriate volume from the max fill point so that there will still be enough room in the tank when the piston retract.

BTW the bypass Flow Meter circuit will not only show when there is a leak FROM the Circuit but will also indicate when there is a valve or other component that is being held open or has been damaged and is allowing fluid to Bypass and return to Tank unnecessarily.

These energy wasting bypass situations often go undetected until they get so bad that the Heat Exchanger can't keep the system at a nominal operating temperature.

Just another diagnostic tool for determining the health of a hydraulic circuit.