Electro Hydraulic Oil Pump pressure is not building up to required pressure

We have Electro Hydraulic system for Steam turbine control valves consisting of two Parker PV15 axial piston Oil Pump where one pump is kept running and other remains on standby condition. Normally the pressure on the pump delivery remains at 140 bar. A week ago, suddenly one pump's delivery pressure reduced to 100 bar and standby one started due to interlocking system. 6 days later, second one's pressure also got reduced and Steam Turbine Tripped. Now we are trying to build up EH Oil Pressure by starting pump. But after pressure increases upto 90 bar, it suddenly gets reduced to 2 or 3 bar although pump is running and stays on that. If we stop the motor and start again, same thing happen (Pressure increases upto 90 bar and suddenly drops to 2-3 bar). A sudden 'ping' sound occurs during pressure drop. Pressure drop happens within second. Both the pump shows same phenomenon. Only difference being for one pump pressure increases upto 90 bar and for another one, it increases upto 65 bar

We have changed the delivery filter. There is a relief valve, non return valve and isolation valve after pump delivery. We have checked Relief valve(Pilot operated) and found no abnormalities. We even interchanged the spring of the relief valve with a solid bar to ensure that oil is not drained through relief valve. But the same phenomenon occurs again and again. We disassembled the pump and found no abnormality.

What can be done now? Hoping for some suggestion.
 
What is purpose /function of these EH pumps?

What frame type is the Steam turbine...Controls system/Governor OEM...

Is there any P&ID available for better assistance otherwise I cannot support remotely...

James
 
1. Purpose of this EH pump is to develop a certain hydraulic pressure for steam turbine governing valves.

2. Steam turbine typel: LN60- 5.63/0.60/527.255
Control valves are hydraulic operated servo valve.

No P&ID available
 
1. Purpose of this EH pump is to develop a certain hydraulic pressure for steam turbine governing valves.

2. Steam turbine typel: LN60- 5.63/0.60/527.255
Control valves are hydraulic operated servo valve.

No P&ID available
Okay

Well we call this system Hydraulic Control Oil system

Without P&ID it is not possible for me to support..
 
A P&ID is really necessary, but in thinking about two "redundant" positive-displacement hydraulic oil pumps there would need to be a check valve arrangement between the discharges of the two pumps to prevent the backflow of one pump into the other. It's possible there's a problem with this check-valve arrangement.

Next, there would usually need to be some kind of relief valve arrangement to protect against overpressurization of the hydraulic system, and if that wasn't working there would be a problem like the one being described.

But, my best guess is that some manual valve in the system is not in the right position, or some check valve or even some solenoid-operated valve in the system isn't working properly or has failed. Why a manual valve you ask? Because when something like this happens it's very common for someone (or multiple people) to suddenly develop an interest in the skid and have a look around and think this or that valve isn't in the position it should be in without actually KNOWING what position this or that valve should be in--and so they move the valve without telling anyone. A thorough check of the valve positions of a skid at a time like this is very useful--if for not other reason than proving the valves ARE in the right position. Or a relief valve has failed. Axial piston pumps are positive-displacement pumps--meaning the flow MUST go somewhere if the pump is running. They aren't like centrifugal pumps (which the majority of most pumps are) which can run dead-headed (meaning little or zero flow. The relief valve must be there in case the swash plate pressure/flow regulator system of the pump fails causing the pressure to build up--OR, the flow has been restricted for some reason. Otherwise, the pump casing will explode or the piping will rupture.

BUT, really, without P&ID there's not much more to say or suggest. If you have an outline drawing this detailed, then it's pretty certain there is a P&ID of the skid somewhere, if not the entire hydraulic system.

Also, the current drawn by the motor driving a pump is proportional to the flow through the pump. Use a clamp-on ammeter to check the currents being drawn by the pumps and compare them against the motor nameplates. If the current being drawn by the pumps is lower than motor nameplate then the flow through the pumps is lower than design; it the current is much lower than motor nameplate the flow is much lower than design--which means that either the pump is bad (it's not impossible for two pumps to fail if some other component in the system failed which affects both pumps!), or some component is not working properly (pressure regulator; flow compensator; bypass valve; etc.).

But, a P&ID is really key. No operator or technician is capable of properly operating, maintaining or troubleshooting any system without a P&ID.

Full stop.

Period.

Best of luck.

Please write back to let us know what you find. A LOT of people read these threads on Control.com, and you will spark the interest of a lot of people, so now you are (more or less) obligated to provide feedback. (And it's only common courtesy that if you ask for help you provide feedback about whether or not the help you received was useful--or not.)
 
Also you did not tell us about ( as asked before ):
OEM/manufacturer of the ST
Controls systems installed /Governor

Is there any alarm annunciated other than Control oil Low pressure...

With more valuable datas the best we can support !
 
Thank you for your reply. To answer your questions,
OEM of ST: Harbin Turbine Company Limited
Control system is also installed by Harbin Turbine Company Ltd. which consists of one Stop valve and one Control valve for HP system and One stop valve and one control valve for LP System. (all of them are hydraulic operated; OEM of the actuator: VTR Vcontorque International Actuator Inc.).

No other alarm annunciated other than control Oil Low pressure
 
A P&ID is really necessary, but in thinking about two "redundant" positive-displacement hydraulic oil pumps there would need to be a check valve arrangement between the discharges of the two pumps to prevent the backflow of one pump into the other. It's possible there's a problem with this check-valve arrangement.

Next, there would usually need to be some kind of relief valve arrangement to protect against overpressurization of the hydraulic system, and if that wasn't working there would be a problem like the one being described.

But, my best guess is that some manual valve in the system is not in the right position, or some check valve or even some solenoid-operated valve in the system isn't working properly or has failed. Why a manual valve you ask? Because when something like this happens it's very common for someone (or multiple people) to suddenly develop an interest in the skid and have a look around and think this or that valve isn't in the position it should be in without actually KNOWING what position this or that valve should be in--and so they move the valve without telling anyone. A thorough check of the valve positions of a skid at a time like this is very useful--if for not other reason than proving the valves ARE in the right position. Or a relief valve has failed. Axial piston pumps are positive-displacement pumps--meaning the flow MUST go somewhere if the pump is running. They aren't like centrifugal pumps (which the majority of most pumps are) which can run dead-headed (meaning little or zero flow. The relieve valve must be there in case the swash plate pressure/flow regulator system of the pump fails causing the pressure to build up--OR, the flow has been restricted for some reason. Otherwise, the pump casing will explode or the piping will rupture.

BUT, really, without P&ID there's not much more to say or suggest. If you have an outline drawing this detailed, then it's pretty certain there is a P&ID of the skid somewhere, if not the entire hydraulic system.

Also, the current drawn by the motor driving a pump is proportional to the flow through the pump. Use a clamp-on ammeter to check the currents being drawn by the pumps and compare them against the motor nameplates. If the current being drawn by the pumps is lower than motor nameplate then the flow through the pumps is lower than design; it the current is much lower than motor nameplate the flow is much lower than design--which means that either the pump is bad (it's not impossible for two pumps to fail if some other component in the system failed which affects both pumps!), or some component is not working properly (pressure regulator; flow compensator; bypass valve; etc.). But, a P&ID is really key. No operator or technician is capable of properly operating, maintaining or troubleshooting any system without a P&ID.

Full stop.

Period.

Best of luck.

Please write back to let us know what you find. A LOT of people read these threads on Control.com, and you will spark the interest of a lot of people, so now you are (more or less) obligated to provide feedback. (And it's only common courtesy that if you ask for help you provide feedback about whether or not the help you received was useful--or not.)

@"WTF?,
When the pump pressure reaches around 90 bar, current taken by motor is 20 amp. When pressure falls to 2-3 bar current taken by motor is 20 amp. Rated current of the motor is 30 amp. During normal operation motor used to take 20 amp.
 
Thanks everyone for all the responses. Still we are trying to understand what explains the sudden pressure drop from pump delivery and how it might occur.
 
Thank you for your reply. To answer your questions,
OEM of ST: Harbin Turbine Company Limited
Control system is also installed by Harbin Turbine Company Ltd. which consists of one Stop valve and one Control valve for HP system and One stop valve and one control valve for LP System. (all of them are hydraulic operated; OEM of the actuator: VTR Vcontorque International Actuator Inc.).

No other alarm annunciated other than control Oil Low pressure
Thank you for these clarifications,

I still did not find any relative informations on that ST model /type ..on the web... also on the Actuator OEM ...

Did you have read teh document that @Dave shared here ...if yes is taht the same OEM that you mentionned ?

I have P&ID on ST but it is ALSTOM model maker (660MW )..What is Nominal power /rating of this unit ?

Would be glad to support you if I could get P&ID...
 
The best thing would be to troubleshoot from /on the ST governor ..i dont have enough informations on that controls system

I dont know Harbin ST governor /control system ...can you provide more details ..
 
Somebody needs to get a P&ID from HARBIN. Or, get out to the skid and start drawing one based on the piping and components on the skid and start checking the suggested devices for proper operation. Condensing or back-pressure ain’t got squat to do with hydraulic oil pump operation. Absolutely not a thing.
 
Somebody needs to get a P&ID from HARBIN. Or, get out to the skid and start drawing one based on the piping and components on the skid and start checking the suggested devices for proper operation. Condensing or back-pressure ain’t got squat to do with hydraulic oil pump operation. Absolutely not a thing.
I was asking about ST type (backpressure or condensing) in order to search on P&ID for such ST type
 
After replacing new pump, problem has been solved. Still don't know what happened with the earlier pump. We disassembled the whole pump including pressure compensator but didn't found any abnormalities in any part of the pump. Can anyone provide some suggestion about where the problem might have occurred in the pump?
 
Thank you for the update.

How long have these pumps—and this hydraulic skid—been operating? Is this turbine being commissioned or was it recently commissioned? If it was recently commissioned, how long has it been operating?

Has the hydraulic fluid temperature been maintained at the specified temperature, or has it been higher or lower than specified? What is the specified temperature and what has the temperature been maintained at? Has there been any problems with the temperature regulating system?

Did you replace one pump or two? Because I think you said both pumps had failed.

Has the “operation” of the hydraulic pump relief valves been checked? Has the current draw of BOTH pump motors been checked—and if so, what are the current draws and what is the rated current draw from the motor nameplates?

AGAIN, the current drawn by an electric motor is directly related to the work being performed by the motor. Rated work is done at rated current draw (both numbers are on the motor nameplate). If the amount of current drawn by an electric motor exceeds the motor nameplate value then the device being driven by the electric motor is requiring more power than the motor is rated to produce.

A particular electric motor should be chosen for a particular driven device based on the rating of the device (not always found on the device’s nameplate). But the supplier of the equipment should have known the requirement of the application when choosing both the device and the motor driving the device.

If the device is requiring more power than the motor driving it is rated to produce either the supplier chose the motor incorrectly or the device—and the motor driving it—isn’t correct for the application. OR the device isn’t adjusted properly.

Usually the electric motor will eventually fail if the current drawn by the motor is excessive (exceeds the motor nameplate value), but sometimes the device can fail if it’s producing more power than it’s rated for. If the axial piston pump is producing too much flow because the relief valve is relieving when it shouldn’t be then the pump may fail prematurely.

We can’t know how the pump was disassembled or inspected but it’s difficult to understand two pumps failing at nearly the same time. It’s possible BOTH pumps and motors were not properly sized for the application—but that means if the same pumps were used to replace the previous pumps they are going to fail as well, eventually.

Best of luck!
 
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