We have diesel generators of 1750kW capacity. They are 16 cylinder V type engine coupled to a generator for emergency power source.Starting of the engine is done by an air motor, which cranks the engine initially for about 4-5 seconds (with a maximum of 8 seconds) after which engine picks up speed on its own. Recently we faced a problem that the air motor which was in service for the past 3 months failed to crank the engine. We replaced the air motor after confirming air pressure was adequately existing for the normal cranking. The second motor successfully cranked the engine. though the problem is solved, being an emergency equipment, we don't want a repeat of this failure. how to confirm that engine is not taking higher torque for cranking. what periodic checks can reveal problems with the engine / air motor. would any one help me. Lot of luv and thanks

Looks like you are trying to find the root cause.

Have you checked the OEM manual about the air motor checks?

Do you run the genset periodically?

You said in service for past 3 months, is it still under warranty period?

Have you inspected the old air motor(removed one) for any damage? What went wrong with it? Just by replacing the air motor with new resolved the problem? Is that the case?

1.was air pressure sufficient at the time of start?
2.was sv energised ?
3.clean the teeth of the gear/pulley of the engine. Foreign material may prevent engagement of motor pinion with gear.
There may be some problem with the control valve . The motors are normally very much reliable and run for years and years without any problem.
regards
irshad

thanks for all the efforts. shall add some more information. There are 2 receivers at 17kg/cm2 and air is drawn to the air motor through a filter and a PRV. PRV regulates the pressure to the air motor to 10.5 kg/cm2. I measured the air pressure at the inlet to the air motor and at the outlet of PRV. We generally start the engine once a week for surveillance testing. Today when we started the engine i have hooked pressure transmitters to measure the air pressures. In the first start, air motor \cranked the engine for about 8 seconds and engine did not pick up speed. When the engine was started the second time, it picked up speed within 8 seconds. This was the case last week also, where we replaced the air motor. i initially suspected higher torque to crank the engine and second start makes the engine to move little freely as it had been turned up during the first start, probably due to lubrication of bearings and cylinders. When i saw the air pressures after PRV and at inlet to air motor, i was surprised to see that in the first start, the air pressure had reached a maximum value of 4kg/cm2 and then started dropping - due to rotation of air motor and the engine. in the second start, the air pressure at air motor inlet was seen to be 7kg/cm2. If the engine had any problem, how the air pressure takes a higher value in the second start. i am little confused. any clarity please. regards.

Jayravi,
There are a number of things to check and obtain evidence, as others have pointed out. In addition,
1. You mentioned a PRV; is that a regulator or relief valve? Normally we do not use PRVs as regulators. Regulators can fail due to a number of reasons - fouled ports, damaged springs or shuttles, leaky diaphragms etc.(depending on construction details, please provide cross sectional drawing). A good regulator should provide rated pressure, i.e. 10.5 barg at discharge on full load.
2.

quote:

We generally start the engine once a week for surveillance testing.

How long do you run the engine during tests and do you put it on full load for at least 1 or 2 hours till the jacket cooling water is hot? It is better to test fortnightly and put the engine on full load during tests for say, 2 hours. Cold running engines can become unreliable and costly to maintain.

CHECK WHETHER EMERGENCY LEVER WAS IN NORMAL POSITION?
THERE ARE SV'S AT OUTLET OF RECEIVER. ITS PORTS MAY BE PARTIALLY CHOKED.
DISMANTLE PRV AND SV TO FIND ROOT CAUSE.
I DO NOT THINK THAT THERE IS ANY PROBLEM WITH THE MOTOR AT ALL.
CHECK PRV PRESSURE SETTING. NORMALLY THERE ARE SEPERATE PRV'S AND SV'S IF THERE ARE MULTIPLE RECIVERS .
PL COME BACK TO THE SITE AFTER YOUR YOU HAVE SOLVED THE PROBLEM. I ALSO WANT TO KNOW THE ROOT CAUSE.
IRSHAD

jay,

In an addition, you have to go through back with your power management system.

When main power went down, the system will automatically compute the system to send signal to the emergency genset to backup few primary equipments. The bulk air compressor which shared by few equipments shall be sufficient to supply presure to crank the emergency genset.

Over pressure of course shall shorten the crank motor life but under pressure also shall bring effect on it even with your genset.

I would like to go through the basic before making an adjustment/repairing with the equipments which shall produce the same results in the future.

Much has been covered except air volume you noted psi. was low at first start, and high at restart?
Psi and CFM are dependent upon each other and system design.
Did you ensure system feed from Bulk air tank through to starter?
All air valves open full?
No tubing Id. change in recent past from maintenance function?
I have known it in the past where small change required extensive troubleshooting .
2'section of schedule 80 was substituted for schedule 40 by a technician and choked system feed about 8%.
Not a lot of loss but just enough to cause intermittant issues after solenoid opened system. <psi?> hope it helps.

Just,
I love this kind of problem solving which will go through the whole line of the system and I did believed that it would much helps on contributing valued data for the RCFA to tackle the root of the problems.

ONE MORE REASON BEHIND NOT STARTING OF ENGINE MAY BE THE GOVERNOR LINKS ARE SLUGGISH. THE RACKS ARE NOT GOING FULLY IN AT THE TIME OF STARTING. CHECK THE ENGINE GOVERNOR CALIBRATION AT SOME WOODWARD SERVICE STATION OR FOR OTHER MAKE. WHAT TYPE OF GOVERNOR IT IS? ELECTRONIC HYDRAULIC OR MECHANICAL HYDRAULIC.
IRSHAD

Is the starter motor a turbine or vane type? Most of the vane type air motors require lubrication, usually injected into the supply air. Does the engine have proper fuel pressure when you go for a start? If not can you manually pump up the fuel system.

wow not sure why it diddnt occour to me before but Ill bet you have a bad injector, or injector pump and your line pressure is dropping out.
I see rough rider beat me 2 it lol good job team!

JUST,
It is a 1750 kw engine. Should be a 12 cylinder engine. One or two bad injectors will not cause problem in starting. There must be fuel injection pumps for each cylinder seperately. If the main spring of any fuel injection pump is broken, then it may cause rack binding resulting in erratic strarting behaviour. Check for freeness of individual cylinders rack by pushing it inside manually.
Regards
Irshad

quote:

Originally posted by roughrider:
Is the starter motor a turbine or vane type? Most of the vane type air motors require lubrication, usually injected into the supply air. Does the engine have proper fuel pressure when you go for a start? If not can you manually pump up the fuel system.

I agree. Most (if not all) of our air motor problems came from not lubricating the motor. It would be the first thing that I checked.

It's easy to check out, have a mechanic open up the air line near the air motor and pour a bit of oil into the line.