DLN 2.0, 9FA GE machine.

purge valve opening / closing time for D5, PM1 and PM4 line can be traced as there's a limit switch installed.

but what about vent valve? there's no limit switch there. our unit has tripped at least 3 times during shutdown (during transition from Pilot Premix to Sub Pilot Premix ie. PM1 + PM4 to D5 + PM1 +PM4)

can someone shed some light?

 

Dinster,

First, I would ask: When did this problem begin? After some maintenance outage?

Second, I've looked through the documentation I have (Piping Schematics and Device Summary) for an early DLN 2.0 9FA and I don't see a D5 device. Without being able to see the Gas Fuel Piping Schematic and Device Summary and likely the CSP I couldn't really hazard a guess as to what it's used for or when it's to be open or closed.

DLN has always been kind of a science project for GE, regardless of what they say about it being a "mature technology." Yeah; it's been around for years, decades now. But, it is still being refined and modified and there are lots of flavors out there that are similar but not identical.

Third, are you talking about some double block-and-bleed arrangement for purging?

If it's not changing state fast enough, it would seem that there is a pressure switch or transmitter somewhere that is sensing a high or low pressure when there shouldn't be? And you're trying to determine what device is not changing state fast enough? Which device, specifically? 20VG-2? 20VG-3? I've seen people install various types of limit switches on these valves, from contact to non-contact (proximity) types (the latter seem to hold up better under high temperature conditions).

Not knowing which device and where the device is installed, it's difficult to tell you to post someone to watch it. A lot of people these days are using video cameras to monitor devices in compartments where they can't send people when the unit is operating. The big consideration for them is low voltage and temperature rating. And access to the compartment to install and set them up, and then to remove them.

It would almost seem easier to replace the valve, or to remove it for servicing or refurbishment at the earliest convenience. I believe some of the vent valves had either very small openings or an orifice or needle valve was used in the outlet to prevent sudden pressure spikes or dips. A lot of mechanics find those little needle valves irresistible to fiddle with.

 

CSA,

i apologize for not providing enough information earlier..

- GE 9FA+e with DLN 2.0+ combustion

- under Pilot Premix, Sub Pilot Premix and Diffusion mode, 20VG-2 will open, VA13-1 and VA13-2 will close

- unit tripped twice due to L4GPFT "GAS PURGE FAULT TRIP" alarm

- VA13-1 and VA13-2 command and feedback is ok (L33PG1C = 0 and L33PG2C = 0 approx. 3 secs after L20PG1ON = 0

- 20VG-2 command ok (L20VG2C = 0 almost same time as L20PG1ON = 0, however no limit switch for 20VG-2

- L63PG1AH still not go to ZERO ie. line is still pressurized

- after 8 secs, unit tripped due to L20PG1ONY becomes TRUE

- during troubleshooting, 20VG-2 found to be smooth, no sticky

- we rule out pressure switch coz 3 nos. of switch cannot be faulty

Appreciate if u can shed some light..

 

dinster,

You seem to be saying there are multiple pressure switches, all sensing a high pressure when the solenoid 20VG-2 is energized.

You say the solenoid valve operation is "smooth". Is it blocked somehow? The installations I've seen use small solenoid valves and small tubing for the vent lines. I think this is because they don't necessarily want the pressure to drop too quickly, but that's just my own guess and I have no data or documentation to support that personal perception.

Something has changed; either there's a blockage somewhere or the tubing is damaged or something is amiss. Because if this just started happening, then there's likely a reason for it.

If the pressure switch(es) indicate the pressure takes a long time to decrease (you should be able to trend how long it does take for the pressure to drop below the switch setpoint(s)), then the challenge is to find out why it's taking longer than it used to and longer than it should for the pressure to drop.