governor positioner link fracture due to high vibrations

[chumet1]

governor valve positioner link stud fractured at the point where the link is joined to the governor actuator. i measured the vertical vibrations on the position shown on the picture attached on different units (units 6 & 7) because they have the same valve design and unit capacity. on unit 6, the one with the fractured link the vibrations were 19mm/s whilst at unit 7 were 13mm/s. we replaced the mild steel stud with a high tensile steel stud and it also broke in 2days i think due to its brittleness. due to the ripped threads we installed an 8mm mild steel thread that is holding on for now. my question is what is the allowable vibration at the governor valve for a 150MW capacity unit and what are the likely causes of these vibrations from your experience. and also possible corrective actions to solve this problem because i believe our solution is just a stop gap measure.

 

[desertfox]

Misalignment, bearing beginning to fail, foundation erosion , foundation bolts loose, that said e don't know anything about the unit other than its 150MW capacity.

It would be useful if you can post a picture of the fractured parts and give us some history and detail of the units

 

[chumet1]

these are the pics i could get. i will try to get history on the unit

 

[desertfox]

the pics not really any help, its dark and I cannot make anything out, other than a bolt thats snapped and there is an awful lot of corrosion which might also be the cause.
We need some proper clear pics of the failed parts and what is the unit, unfortunately unless we get some clear and proper information no one here will be able to help much.

 

[chumet1]

tahnks for your assistance. after taking another route in my investigation and my solution implementation i think i have to repost focusing on the new route that i have taken in troubleshooting to get assistance on how to come with the solution

 

[byrdj]

is this an original design link or is it something new?

as for the vibration, is the vibration the modulation of the actuator or is the whole valve assembly resonating from the turbine vibration. If resonating from turbine, is the turbine vibration level excessive and thus a balancing needed. if the turbine vibration level is acceptable, then it is possible there is a support hanger problem. I have seen many valve support bases break free from the fondation concrete.

if it is actuator modulation from the control system, then it depends upon what type of controls you have. determining the frequency would help identify where to look. for example if the unit has a flyball governor, its rotational speed is about 9 hertz if there is a worm wheel problem

Using your representation of the connection from the post in "mechanical engineering other topics", that is a classic design error for levers and links. "there should be no transfer accross a thread". I'll assume the positioner link is turned to tighen it up against the position yoke. I'll also assume the outer radius of the yoke was at least spot faced for the end of the rod to make full face contact. for this type of connection, I would highly recomend that the positioner link be fitted into the a bore into the yoke. I would also reduce the inside diameter of the positioned rod so that it makes contact on just the outer diameter. this fit should be a slight interferance or size to size with the outer diameter of the positioner link making a 100% contact on the face when torqued down.

that design would not be my preferred. If for some reason, it is believed the LVDT must be near the actuater main push rod (center) then using a flate plate arm with the base under the main nut would be better. also the bolting for the LVDT's rod end bearing must not have and threaded section going accross a joint. a more preffered would be reduce the cantilever due to the lenght of the positioner link by moving the LVDT over to the lift rods on the side. I can not provide exact preffered loacation with out more details of the valve assembly