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Can anybody explain the complete mechanism of Ratcheting Self sequencer VH14-1 of Gas Turbine?
O
Olayiwola
> Can anybody explain the complete mechanism of Ratcheting Self sequencer VH14-1 of Gas Turbine?
Did you mean VH14? The Hydraulic Ratchet Sequencing Valve? It perform the sequential supply of hydr. oil to the ratchet mechanism to perform effective forward and reverse stroke ratchet during cooldown of a gas turbine. I think i also need someone in the control and instrumentation dept to explain the principle. someone pls expatiate
Did you mean VH14? The Hydraulic Ratchet Sequencing Valve? It perform the sequential supply of hydr. oil to the ratchet mechanism to perform effective forward and reverse stroke ratchet during cooldown of a gas turbine. I think i also need someone in the control and instrumentation dept to explain the principle. someone pls expatiate
I don't have access to a Starting Means Piping Schematic (P&ID) at this writing, but I'll take a stab at trying to describe how it works.
It would be best if you would describe the problems you are experiencing and we could provide a more concise answer, and if you wanted more detailed information than we provided you could ask and we are usually more than happy to provide it.
The self-sequencer was developed to reduce the need to have additional pressure switches and other sensing and control devices in order to operate the hydraulic ratchet mechanism. The self-sequencer directs the flow of high-pressure fluid (lube oil) from the ratchet pump to forward stroke pistons (there are usually two of these) or to a retraction stroke piston (there is usually only one of these). When the pistons reach the end of their stroke the pressure in the system builds up and when the self-sequencer sees this pressure rise it changes the direction of fluid.
When the ratchet reaches the end of a forward stroke and the pressure increases when the piston no longer moves, the self-sequencer switches the direction of fluid flow to the retraction stroke piston AND actuates a limit switch (33HR-1) which "tells" the Speedtronic that the end of the forward stroke has been reached.
When the retraction stroke piston reaches the end of its stroke and the pressure builds, the limit switch 33HR-1 is de-actuated and the fluid flow is re-directed back to the forward stroke pistons for a few seconds (this time is controlled by the Speedtronic) and then the ratchet pump is shut down while the (usual) three-minute time between ratchet operations times out.
After the three minute timer expires, the ratchet pump is re-started and the process begins again.
The purpose of the short forward stroke after the retraction stroke is to try to ensure the teeth of the jaw clutch remain engaged. Sometimes, the jaw clutch teeth can become disengaged, either slightly or fully, if the shaft "jumps" during the ratcheting. So, the designers chose to have a short forward stroke after the retraction stroke and before the pump is shut down for the (typical) three-minute time delay between ratcheting to try to keep the jaw clutch teeth engaged.
Prior to the development of the self-sequencer, there were two pressure switches and a solenoid-operated valve necessary to operate the ratchet mechanism.
The self-sequencer needs to have clean, filtered oil because some of the internal passages are not very large (pilot-operated spools and such). Most of the filters provided by the turbine packager did NOT include any differential pressure gauges or indicator, and consequently many of the filters get so plugged they rupture, releasing lots of dirt and contaminants at once into the self-sequencer's internal passages. It's always a good idea to install some kind of differential pressure indicators, and to change the filters when necessary.
Most of the ratchet systems as provided by the turbine packager also did not include any pressure gauges in the lines. So, it's a good idea to install at least one gauge (on the discharge of the pump at a minimum) and to record and monitor that pressure so that if problems do arise there is baseline data to refer to.
Lastly, the reason I mentioned the Starting Means Piping Schematic (P&ID) is that, typically, there is a manual valve (VM2-1, I believe) that needs to be in a particular position in order for the ratchet pump discharge pressure to be ported to the hydraulic rams that close the jaw clutch halves to engage the jaw clutch teeth. It's very common for people to accidentally "kick" the valve handle (which isn't usually very well identified and is usually at foot level) which results in problems with ratcheting operations. So, be sure to check the manual valve to be sure it's in the proper position. Every time the ratchet pump is energized there should be a solenoid, 20CS-1, I believe, that ports a small portion of the ratchet pump discharge pressure to the jaw clutch closing rams to make sure the jaw clutch halves engage (presuming the manual valve, VM2-1, if I recall correctly, is in the proper position).
Again, if you would describe the problem(s) you are experiencing, we could probably provide a more concise answer. And any details you required.
Have a look at the Starting Means Piping Schematic (P&ID) and the 'Starting Means' System Description in the service manuals provided with the turbine when it was new. You may also find more helpful information there.
If you need more information, let us know.
It would be best if you would describe the problems you are experiencing and we could provide a more concise answer, and if you wanted more detailed information than we provided you could ask and we are usually more than happy to provide it.
The self-sequencer was developed to reduce the need to have additional pressure switches and other sensing and control devices in order to operate the hydraulic ratchet mechanism. The self-sequencer directs the flow of high-pressure fluid (lube oil) from the ratchet pump to forward stroke pistons (there are usually two of these) or to a retraction stroke piston (there is usually only one of these). When the pistons reach the end of their stroke the pressure in the system builds up and when the self-sequencer sees this pressure rise it changes the direction of fluid.
When the ratchet reaches the end of a forward stroke and the pressure increases when the piston no longer moves, the self-sequencer switches the direction of fluid flow to the retraction stroke piston AND actuates a limit switch (33HR-1) which "tells" the Speedtronic that the end of the forward stroke has been reached.
When the retraction stroke piston reaches the end of its stroke and the pressure builds, the limit switch 33HR-1 is de-actuated and the fluid flow is re-directed back to the forward stroke pistons for a few seconds (this time is controlled by the Speedtronic) and then the ratchet pump is shut down while the (usual) three-minute time between ratchet operations times out.
After the three minute timer expires, the ratchet pump is re-started and the process begins again.
The purpose of the short forward stroke after the retraction stroke is to try to ensure the teeth of the jaw clutch remain engaged. Sometimes, the jaw clutch teeth can become disengaged, either slightly or fully, if the shaft "jumps" during the ratcheting. So, the designers chose to have a short forward stroke after the retraction stroke and before the pump is shut down for the (typical) three-minute time delay between ratcheting to try to keep the jaw clutch teeth engaged.
Prior to the development of the self-sequencer, there were two pressure switches and a solenoid-operated valve necessary to operate the ratchet mechanism.
The self-sequencer needs to have clean, filtered oil because some of the internal passages are not very large (pilot-operated spools and such). Most of the filters provided by the turbine packager did NOT include any differential pressure gauges or indicator, and consequently many of the filters get so plugged they rupture, releasing lots of dirt and contaminants at once into the self-sequencer's internal passages. It's always a good idea to install some kind of differential pressure indicators, and to change the filters when necessary.
Most of the ratchet systems as provided by the turbine packager also did not include any pressure gauges in the lines. So, it's a good idea to install at least one gauge (on the discharge of the pump at a minimum) and to record and monitor that pressure so that if problems do arise there is baseline data to refer to.
Lastly, the reason I mentioned the Starting Means Piping Schematic (P&ID) is that, typically, there is a manual valve (VM2-1, I believe) that needs to be in a particular position in order for the ratchet pump discharge pressure to be ported to the hydraulic rams that close the jaw clutch halves to engage the jaw clutch teeth. It's very common for people to accidentally "kick" the valve handle (which isn't usually very well identified and is usually at foot level) which results in problems with ratcheting operations. So, be sure to check the manual valve to be sure it's in the proper position. Every time the ratchet pump is energized there should be a solenoid, 20CS-1, I believe, that ports a small portion of the ratchet pump discharge pressure to the jaw clutch closing rams to make sure the jaw clutch halves engage (presuming the manual valve, VM2-1, if I recall correctly, is in the proper position).
Again, if you would describe the problem(s) you are experiencing, we could probably provide a more concise answer. And any details you required.
Have a look at the Starting Means Piping Schematic (P&ID) and the 'Starting Means' System Description in the service manuals provided with the turbine when it was new. You may also find more helpful information there.
If you need more information, let us know.
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