Priming Lube Oil Pump

Why don't you take a shot at it first. You MUST have some ideas about what needs to happen, and when. Think it through, just like we would do.

I'm assuming that you have a "priming lube oil pump and the mechanical oil pump in a ship engine" before you. Most of us do not, so you already have an advantage.

So, go ahead, we're waiting.

Your question could be formulated in more detail, but I will give some information that may help.

I have only come across this type of set-up on smaller, high rpm engines started with compressed air. The "control sequence" could be described as follows:

When you activated the start this activated an air driven priming pump first, and when the lube oil pressure had built up the pressure switch activated a solenoid valve that permitted compressed air to enter the air driven starter motor. As soon as the engine started to rotate the mechanical lube oil pump "took over" and provided the lubrication necessary.

This set-up was to prevent damager to the engine bearings. As I recall it, this was a Caterpillar engine.

Best of luck

Gunnar "Gus" Gustafsson

www.documates.com

Hi ajaith2901,

There are two principal reasons for having a 'priming' pump,firstly for pre-start lubrication and secondly for post-shutdown cooling of the turbo charger bearings.

The first function would be programmed into the start-up initiation cycle and prevents starter operation until oil pressure is established.

The second function is initiated during the run-down phase (as fuel is cut off) and sustains pump operation for say 10minutes ater the engine has stopped. The turbo spinde and seals are there-by protected from a build-up (cooking) of heat from the energy left in the turbo casing.

These applications are found in both large slow speed engines (ie marine derivatives) and high speed units found in railway power plants and CHP type applications.

You should look at the likes of GE and Sulzer applications for more info.

Happy New Year.

Massey.

On larger high speed diesel engines (twin screw) with electric starters (axial type-2 per engine)...........on pressing the start button, a motor driven oil pump started up..........when the oil pressure reached 30 p.s.i a, pressure switch closed allowing battery starting current to the starter motors........brrrrmmmmm..........engine started, power to M/D pump shut off.........engine driven lub-oil pump takes over.

On large slow speed marine diesel engines, all oil pumps, jacket cooling pumps, piston cooling pumps, etc., are all driven by electric motors.........no water cooling or oil pumps are driven by the engine.

The coolant and oil tanks have either steam or electric heaters (generally steam) and as the liquids are slowly heated the pumps circulate water or oil around the engine and gradually bring the engine up to its optimum operating temperature, before starting.

Engine warm up from cold is approx. 24 hours. This allows the huge mass of metal used in engine construction to warm up slowly and evenly..............this prevents cracking due to unequal expansion.

When the engines are running, oil and coolant temperatures are maintained by sea water (supplied by M/D s/w cooling pump) cooled heat exchangers. Engine shut down usually took about half an hour.

Most merchant ships when coming into port only drop their engine temperatures to a stand-by condition.........only takes about an hour to be ready to proceed to sea.

Dear Massey... Thanks for the reply .. My situation is there is a priming pump when the engine is started in auto mode this will start circulating the lube oil and the pressure starts building up , once the pressure is aprox 20.4 bar the priming pump stops and the auxiliary pump which is coupled to the engine is able to deliver the required pressure . Once the RPM is dropped ,the priming pump should start only after a fixed time (there is a timer) . But now what is happening is the priming pump is not getting cut off in auto mode as hence i have to post some one to stop the priming pump and there fore not able to put the control in auto mode .The control is done by pressure switches and there are 4 of them , since no drawings are available i am not able to check the ckt . My assumptions are either the pressure switch is faulty or the timer is faulty . Have anyone of you came across similar situations . Thanks in advance

Hi ajith2901,

Presumably the oil pressure switch is mounted on the engine and is subject to vibration so it may well have become defective. Your timer will be in the control cabinet so is probably better protected. You could set up a trial to simulate the changeover condition and therefore test the pair of them.

Good hunting,

Massey.

As I stated in my earlier reply, your question should have some additional information added to make it easier to reply. To find out what type of engine (manufacturer) would be helpful.

First you mentioned that there was a pressure switch and I assumed there was only one. To have four pressure switches and an automatic start sequence makes me understand that it is a more sophisticated set-up then the simple (but quite ingenious) set-up on the Caterpillar engine.

I have some experience with Wartsila Diesel engines, and many of those are used in power plant set-ups with completely automatic start.

These units use electrically driven pre-lube pumps and they were started as programmed into the automatic start sequence (where other conditions must be met as well, such as correct jacket water temperature and oil temperature before the start could proceed).

The pressure switch would sense the minimum required oil pressure before the start was permitted (but I wonder if your 20.4 bar is correct. It seems to be a bit high for a circulating system). When the correct pressure was reached the start was permitted. The other pressure switch controlled that the normal (higher) operating pressure was reached withing a set time limit. If not the start was aborted.

When the correct operating pressure was reached this also shut down the pre-lube pump.

There were other pressure switches as well...one to give alarm at low oil pressure and another to activate a shut-down sequence should the pressure become too low to permit safe operation.

All of these functions were hard-wired to ensure safety in operation.

If I were you I would contact the manufacturer and demand to get a copy of the correct control sequence - and also a copy of the correct engine parameters. This as I believe the lube oil pressure set for the pre-lube pump (as you wrote as 20.4 bar) may be incorrect. Incorrect settings of the pressure switches can give the problems you describe.

When you do contact the manufacturer, don't forget to give full details of the engine, the type, year of manufacture, serial number, etc. This as there often are design changes to units and thus it is important for the manufacturer to know exactly which unit you have problem with.

Best of luck

Gunnar "Gus" Gustafsson

www.documates.com

Dear ajith2901,

Firstly I must question the 20.4 barg pressure for the lube oil system this is well above anything I've ever heard of for such plant. Could the decimal point be in the wrong place? Given that you are probably monitoring a number of oil related conditions the presence of multiple pressure switches is not necessarily unique. Excess pressure is as undesirable as very low pressure and therefore the daisy chain of switch contacts should be checked using simple continuity logic.

Given that there may be a pump latching relay to initiate or sustain operation on a fail-to-start condition then the pressure switch line-up becomes more apparent. Remember also that if you have electric pre-heating of the jacket cooling system then intermittent priming oil pump activity is a feature in some engines.

Best wishes,

Massey.

Hi ajith2901,

Sorry for being incognito in the last post! I note on rereading your reply that you think the timer functions in a delay-on mode I would have expexted delay-off. As many of these timers have a selectable MO (using dip switches etc) you may wish to consider this line of reasoning It is consistent with both the failure to start (ie reach full speed) and avoids premature stopping of the pump and possibly leading to a lube oil pressure fail alarm status being generated.

I'm sorry if this appears only to confound the situation but there are so many variants out there covering many different applications that trouble shooting yours (effectively) is extremely hit and miss.

Let me know how it goes.

Best wishes ,

Massey