This article is about trouble-shooting the mechanical connection between an Actuator and a Butterfly installed on a Reciprocating (Piston) Gas Engine.
It is based on the use of a Woodward UG8 but generally applies to all mechanical governors used.
Description of the practical problem you're facing
Problem with controlling speed:
- hunting the rods is jigging around
- always seems to be moving backward and forwards (Control area to fine)
- trying to control in a few degrees of travel
- Poor synchronization
Mechanics mess it up and play with the setting, your engine won't start.
The Woodward UG8 stands for:
- 8 ft/lbs on the governor arm coming of the governor lever coming of the spindle.
All governors & actuators are very common to the UG8, we come across many makes but the following steps work on all similar governor set-ups in their basic task to control speed in a stable manner.
What did you see?
The linkage on the throttle arm is using the hole in the leaver closest to the spindle. This is a problem: More force is required to move the throttle plate as you have less leverage plus the governor has to move more to open the throttle moving the link bar further away from the spindle.
Use the 1st one furthest away from the spindle you know have more force working on the throttle and small movements on the gov/acc have a greater movement on the throttle plate giving better control.
Take off the linkage from the governor/actuator/throttle butterfly renew any worn parts you want a positive action, to be transmitted along this linkage.
This is the procedure to configure the linkage:
- Throttle butterfly in the idle position resting against the stop.
- Gov/acc in the shut down idle position.
- Move any leavers on the Gov/acc, so that they are working with the throttle arm try to get the arms in the same positions, if the butterfly arm is at 45’ deg mimic with the Gov/acc
- You have 47’ degrees of movement on the Gov/acc so you should try to get this to correspond with the throttle arm to max full open position
- Fasten the throttle bar to the throttle butterfly arm on it max point away from the spindle better leverage less force required.
- With both throttle and Gov/acc in the idle position adjust the length of the bar to fit both lever arms.
- Trying always to get the largest lever action on both leavers.
- It may take time to find the best holes in the leavers but the aim is to have as long as possible leaver, and max movement from Idle to full RPM.
- Now you have increased the leaver length the Gov/acc has more of the 47’deg arc to maintain the desired RPM. If you have a drop in load the governor /actuator can respond.
- Start the engine using the hand throttle slowly allowing the engine speed to increase. As you near the desired speed you will see the Gov/acc start to take over and going back to a controlled speed. You will now find the Gov/acc has more useful range of its 47’deg and not try to control the engine in 5’deg, it responds to load changes better and will have less of a swing up down
Hunting and all funny controls issues disappear, it takes less then 30 minutes!
When you've got 3 units trying to sync, all with different set-ups, you have no chance getting a smooth synchronization! One unit will chase the other. Do all the units as described above. It cost nothing except a little time.
I have had engines going down on over speed caused by wrong linkage set-up converting a very small movement of the actuator into a large butterfly movement.
Night mares, just to see how many units are not the same, for starters actuators' that go from below the horizontal into the vertical.
How do you get a common movement! There is a point either side were little of no movement occurs and this is where you won't control.
Below are photos of three machines: Linkages all different but all have good position of the arm.
Good arc of control movement is linear at all points of control.
About the Writer:
John Gill is an Oil and Gas Professional who has been involved in Maintenance of Reciprocating Compression & Power-Generation Machinery for many years.