How to explain hydrolock in a diesel engine?

[Pengze]

Actually what is a hydrolock? And how does it happen? Can the hydrolock damage the engine piston & con-rod?
Does the defective fuel pump anything to do with the hydrolock problem?
Kindly explain in details & thank you.

[The Dieselduck]

This is a pretty basic question I think. Which is why we always blow an engine out before starting. Certainly a fuel pump, but I believe the injection valve is to blame for most of these occurrences. The injector leaks; a fair amount of fuel builds up, and you go to start the engine and the force from another piston firing is too much for the piston with the fuel in it. The fuel has nowhere to go and cannot be compressed, therefore the connecting rod bends or the crank throw slips, or break if its not press on, and so one and so forth, beaucoup dommage.

[Matthias]

Anyone ever have this happen to them onboard? Is the indicator cock enough of a port to allow whatever fluid (fuel or water) trapped inside your cylinder to escape before it does any serious damage?

[JK]

I've seen the pre-lube pump left on too long with Fairbanks Morris engines and have LO shoot across the space when the engine rolled over with the cocks open. It is not pretty and leads to a lot of unhappy people.
I have also seen it with water when there is a liner or head problem.

[Sébastien]

In response to Matthias, although it has never happened to me personnally I can state that no, the indicator cock may not be enough to let all the fluid escape during the upstroke. This means that even with your indicator cocks open and free it is still possible to warp the engine crankshaft when attempting to blow over the engine on air if there is a lot of liquid. Your best bet to prevent this is turning the engine on turning gear for ten minutes before you blow it on air, that way if there is liquid present in any cylinder your truning gear motor will stall. If you go to disengage your turning gear and you notice that the engine is no longer turning you must investigate further. Sébastien

[Matthias]

That's what I also thought, Sébastien. However, on every vessel I have so far sailed on it has never been a routine practice to actually turn the engine over using the turning gear before starting it. Blowing through the engine was the norm. However, most of my sailing has been with multi-engine arrangements where the longest run in between starting and stopping an engine is a couple of days. I suppose it would be something that is done on larger single engine setups.

[Madzng]

It is good practice to turn any engine that has not been run for a period of time. In the past engines were always turned on gear, or by hand, prior to starting. As engines have got more reliable and automatic start arrangements have become more common place, this practice has become less frequent.

The period of time depends upon the circumstances, experience of the engineers and history of the engine. Any engine suffering hydraulic lock, is an expensive failure and needs to be avoided, regardless of how many engines the ship has.

Generally I have always ensured that the auxiliary engines not run are taken off automatic stand-by and turned on gear weekly, with the cocks open. This is not only to ensure good lub oil distribution, but to also ensure that the combustion chamber is not filling with liquid. It is also good practice to turn the main engine regularly when the ship is going to be sat idle for a period of time.

Direct drive diesels can be stopped for an hour or more when a ship is in a lock, or when waiting for a pilot to arrive. Some large two stroke engines have a slow start system, which is activated when the engine is not started after a short period of time (20 - 30 minutes). The slow turning system is designed to turn the engine slower than a normal start, once the safety system has confimed that the engine can turn freely (approx 2 revs), the full start air pressure is admited and the engine started as normal.

When sat at anchor for a waiting period with the engine on bridge control, the deck department will be requested to start and stop the main engine every thirty minutes, this is simply to prevent try and prevent enough liquid accumulating in the combustion chamber, to cause damage.

All of the above is on the assumption that small leaks will be discovered, before they get large enough to cause serious damage. Small leaks would hopefully be seen via the cocks, or increasing cooling water consumption. Large or rapird failures will nearly always cause damage unless the ship is very lucky. Following the engine makers instructions and only using authorised spares will help prevent these situations occuring

Would suggest that the most common liquid entering the combustion chamber would be cooling water, through a leaking exhaust valve seat, cracked head/liner or through a turbocharger casing crack. The larger the engine the more noticable the drop in header tank level would become. A leak could also be indicated by a rising sump level, by excessive gassing of the cooling water system or even by a rising and falling of the header tank level.

[Sébastien]

I totally agree with Madzng. Basically if an engine is large enough to have a turning gear fitted, it should be used prior to start up regardless of length of voyage. The ship I sail on regularly does two voyages per week yet we use turning gear before every start up. You have to perform pre-start checks on the engine anyway, simply engage turning gear before pre-start checks and remove turning gear when you have completed your checks (second generator online, oil mist detector test, etc.). You can never be too cautious. Sébastien

[Pengze]

Ok ! This is interesting. Let's ponder & think of the below mentioned scenario.
Now there arises the emergency unberthing from an oil terminal & the pilot is already on board.
Then you found out that one of the cylinder head cracks & leaking cooling water into the combustion chamber(filled up) & you couldn't start the engine.
Consequently, you open the indicator cock & turn the engine & blow thru but the water cannot be expelled completely because of heavy leakage.
My opinion would be, to shut off the header tank supply valve then drain off the water from the upper section only of the cylinder block, keep open the indicator cock of the leakage unit & start the engine.
After the engine has started, I reopen the header tank supply valve & replenish the header tank. Then I inform the bridge to go on slow speed & proceed to anchorage for repairs.
I wonder if this procedure is correct or maybe there are some other alternatives out there.
Remember, gentlemen, this is only for emergency situation!
I would appreciate if anyone could give some comments regarding the above emergency procedure.

[Sébastien]

In the scenario you described, first of all you will not be able to drain the water out of your combustion chamber fast enough to start the engine in any reasonable length of time. Secondly any water leaking into the cylinder will turn to steam in your combustion chamber and wipe away all lubrication and your piston will probably seize before you make it to the anchorage zone. Tankers are required to have steel 'fire wires' to enable the ship to be pulled away from berth with a tug in emergency scenarios such as the one you just described.

[conrod]

Taking this back a step or two..............indicator cosks are not large enough to allow a full compustion chamber of water out for sure !!!

During one of my last voyages deep sea, I had 3 scavenge fires, and a hydraulic lock !! This obviously was as a result of a scav fire.

Picture a Force 9 in the Taiwan Strait, afternoon smoko, and from the duty mess it sounds like a helicopter flying over head !! This was infact the sound from the exhaust of a rather old, East German built, MAN / B&W, SS2S, of about 800 mm bore, under piston scavenging on aft 4 cylinders.

We had a fire raging, in what appeared to be # 4 cylinder. As we slowed the revs and did all the normal stuff, the fire spread, and before long we had a raging inferno. At this point, as a first trip 3/E, I was intrigued to see my engine bursting into flames, and as I walked behing to see all these bright red air pipes, and scavenge doors, I was pretty blown away. Just as I cleared the front of the engine, the under piston air cooler melted, and dumped a " rather large quantity of sea water " into the scav areas. As # 1 cylinder was on the up stroke, it filled up first and as it approached TTD, the relief valve lifted, and spewed forth a large qty of very hot sea water. I just happened to be underneath this. I was not scalded, but did look like a cooked lobster.

Anyway, as I am sure you guessed, the engine now stopped, and the fire went out.

Shortly after, we opened up the scav manifold door on the cooler. It was then you really get a picture of how much " air " space there is, in a large SS2S. It raged like Niagra for a good 10 mins.

Over the next 18 hours, we opened up the engine, changed all the scav valves, blanked of the under piston cooler SW lines, hung # 4 piston, changed the relief valve on # 1 and SLOWLY steamed to a safe anchorage. Once anchored, we pulled # 4 piston completely, and dropped in the spare. Changed the cooler stack (something tells me it was expected as we always had that spare) and 6 hours later we were on our way to Shanghai at full speed again.

Within the year I sat my C/E's ticket at Warsash, Southampton, and got bogged down on a question about " what to do during a scavenge fire on a large 2 speed, 2 stroke "............dont walk round the front !!

[Sébastien]

Wow Conrod, somehow I am glad that I never had as much 'fun' as you during an engineering watch at sea!

[JK]

LOL
Must admit, my thought was, I am sooo glad I missed that experience!

[conrod]

I was only on that vessel for 4 months, and then we sold it to an outfit from China..........handing over in San Fran........and they were not really interested in any of the history.

I believe the vessel is still sailing around, but as far as my company then was concerned, they were glad to get rid of it. The sister ship was with us for a little longer, but she had a charmed life. Where as we were on time charter doing pulp runs from Norway / Sweden to China / Korea, then steel from Japan to the US...........our sister was trading a liner run from Hong Kong through the " islands " to Kiwi. Lots of port time, and good ports to boot !!

It was a trip to remember for sure. When I joined, I had been in Brazil on leave, flew to Norway to join (+33 C to -33 C in 3 days), did a passage in an ice convoy, parked up in Sweden to load the pulp.......actually frozen to the jetty.........then the fires etc, storms, a good run up the road in Portland..........for some, I was on duty, and then getting picked up by the police in San Fran for rolling my own smoke.......not bad for a first trip 3/E eh !!

[JK]

and then getting picked up by the police in San Fran for rolling my own smoke.......

LOL...that must have been a shock!
You know that the rest of the world would never believe a book written about all the weird things that happen while going to sea. They would think it was a fantastic work of fiction.
Meanwhile, mariners would be nodding their heads, laughing and saying, yep, I remember that!