Q: purging cylinders and priming before starting diesels?

A large engine is rolled over with the compression released to flush out any water that may be in the cylinders due to a gasket or o ring leak prior to trying to start it. Water is not compressible so if the engine is cranked with water in the cylinders it can blow out the head gasket or bend the connecting rods.

Not sure what the reference to priming is. A Caterpillar engine can be difficult to start when it is cold. So the cylinders can be heated by spraying in ether.  The ether is easier to get to burn than the diesel, so the ether burns heating the cylinders, then the diesel will burn.

In years past I had some experience with a Caterpillar engine in a wrecking derrick that had a gasoline starting engine. To start the diesel the little gas engine was started first. They shared the same cooling water so by letting the gas engine run for a while it helped heat up the diesel engine. Then, with the compression released and the fuel shut off on the diesel, the clutch was engaged and the gas engine would start rotating the diesel engine.  I would let this go on until the oil pressure came up on the diesel engine.  Next, I would close the compression release and let the diesel spin for a while. This heated the cylinders on the diesel engine.  Then the diesel fuel was turned on and the diesel engine was running. This popped out the clutch on the gas engine.  The gas supply to the gas engine was shut off and it shut down when it ran out of gas. The only problem with this whole process, other that it took a little time, was that the gas engine was started with a hand crank.

David Johnston is correct.  Possible leaks of coolant or fuel into the cylinders are why the engine is turned over with the petcocks open.  Radial airplane engines provide that by turning them over by hand in case oil has filled a cylinder.  Most big engines have that potential problem.

On an EMD engine the fuel injection system is a return to tank system.  More pressurized fuel than is needed for combustion is provided to the fuel rails and what isn't used is returned to the fuel tank.  Priming eliminates air bubbles and makes sure the fuel system is full by circulating fuel through the rails and back to the tank.  In the winter the warm fuel coming back from the engine helps keep the fuel in the return area from gelling so it flows.  There's actually a little built in well in the fuel tank where that happens to concentrate the warmth and liquify nearby fuel for the suction inlet.

"Purging" - Hah! "Priming" - yes.
Opening those purge cocks? You'll never see that happen when a crew member starts an engine! But yes, we do prime the engine before starting.

@Dougklink posted:

David Johnston is correct.  Possible leaks of coolant or fuel into the cylinders are why the engine is turned over with the petcocks open.  Radial airplane engines provide that by turning them over by hand in case oil has filled a cylinder.  Most big engines have that potential problem.

But why is this behavior expected in a "big engine" and not a small one?  If a "small" engine has a head gasket blow and drip coolant into a cylinder, it's considered a major issue (plumes of steam and coolant smell in the exhaust) and a sure sign the block needs service immediately to prevent a blowout. You'd figure it'd be even more important in those super high compression engines. Pools of oil/fuel/coolant in the bore of the cylinder is traditionally considered a stopping point, unless you have absolutely no choice...

@Homey B posted:

But why is this behavior expected in a "big engine" and not a small one?  If a "small" engine has a head gasket blow and drip coolant into a cylinder, it's considered a major issue (plumes of steam and coolant smell in the exhaust) and a sure sign the block needs service immediately to prevent a blowout. You'd figure it'd be even more important in those super high compression engines. Pools of oil/fuel/coolant in the bore of the cylinder is traditionally considered a stopping point, unless you have absolutely no choice...

Please remember that the medium speed diesel engines you are referring to (EMD and GE) have individual power assemblies (cylinder assemblies) with various external water, fuel and lube oil connections. The EMD 2-stroke cycle engines, for example, might have a small internal water leak, when the engine is cold, thus seeping some water (EMD engines do NOT use anti-freeze) into the power assembly, and collecting on the piston crown. The practice of "blowing out" the cylinders with the test cocks open, prior to starting, after the engine has been shut down for many, MANY hours, has always been a safe idea.

@Homey B posted:

But why is this behavior expected in a "big engine" and not a small one?  If a "small" engine has a head gasket blow and drip coolant into a cylinder, it's considered a major issue (plumes of steam and coolant smell in the exhaust) and a sure sign the block needs service immediately to prevent a blowout. You'd figure it'd be even more important in those super high compression engines. Pools of oil/fuel/coolant in the bore of the cylinder is traditionally considered a stopping point, unless you have absolutely no choice...

It’s to protect the very very expensive giant engine!….liquid in any solid form in a cylinder can be catastrophic. The smallest amount in a diesel engine is even more hair raising. A gasoline engine with its lower compression ratio might not get destroyed if there’s a drop or two in the cylinder, but a diesel relies completely on compression to ignite the charge. ( some have cold start igniters, glow plugs, etc, etc, ) If the small engine in your car windows the block due to an ingestion, you’re out 5-10K, If the giant  locomotive diesel tosses a rod out, the railroad could be looking at hundreds of thousands of dollars, by the time the railroad is done with parts & labor …..

Pat

@Big Jim posted:

"Purging" - Hah! "Priming" - yes.
Opening those purge cocks? You'll never see that happen when a crew member starts an engine! But yes, we do prime the engine before starting.

If it is so important then why will we "never see that happen (opening purge cocks) when a crew member starts an engine"? Is this statement just because these engines have not been sitting unused long enough for water to leak? Very interesting thread BTW!

My last job was in transit. In the shops we had two different crafts that worked on the cars. They are Transit Vehicle Mechanic (TVM) and Electronic Technician (ET).  What was the difference?  One got there hands dirty and the other did not.

The locomotive manufactures have something called creepy crank.  This is were, when starting an engine, the starter turns the engine over very slowly for the first revolution.  The idea is that if there is liquid in the cylinders and  the engine is going slowly enough that it will stop turning rather than blowing the engine apart. Locomotive engines use to be left running continuously.  This eliminated a lot of starting problems and kept them warm so they would not freeze. Then fuel became really expensive, so shutting the engines down became important. Where I worked we welded a tee handle on all the cylinder cocks so they could be opened with out any tools. But some crafts just will not get their hands dirty, so a lot of effort went into trying to make the engines more restart friendly. Some times it works, some times it does not.

It's this simple- how many of these videos commonplace on the internet are of engines being started that belong to museums and other restoration groups with limited budgets? It's not even just that, it's the difference between risk.

Also add, these may be policies and checklists of these organizations. In other words, if the employee or volunteer starting this engine causes damage, and it was found they didn't follow ALL steps of the extended safety checks and startup sequence- they are gone.

These are big expensive and harder and harder to repair engines, not to mention costly. Some of them have significant age and wear. Some of them may not be in perfect ideal overhauled shape. Add to that the organization or company may not have the money to repair and are extremely risk averse, they demand and make policies and additional safety steps to protect the equipment and extend it's lifespan. Some of these engines might be used infrequently and thus because of the unknown state or condition of the engine- again being risk averse- demands you perform extended checks and sequences "just in case".

So sure, you personally might not pull your spark plugs and spin the engine over every time you leave your driveway. However, if you had a company vehicle, or were volunteering for an organization, and they said as a policy you will chock your wheels, you will follow all extended startup and testing sequences, by golly- you are going to do it- each and every time.

Not sure what you mean by "big" engine. On the Wilmington & Western we open the cocks and spin the engine the first startup of the day on our SW-1. If it gets turned off and back on again later that day, we just start it.

@Ken Wing posted:

On the Wilmington & Western we open the cocks and spin the engine the first startup of the day on our SW-1. If it gets turned off and back on again later that day, we just start it.

Hmm, that sounds suspiciously like a "policy" or maybe an SOP......... something that is trained, expected, maybe even on a checklist or written down. Something that is trained from one operator to the next.

@Vernon Barry posted:

Hmm, that sounds suspiciously like a "policy" or maybe an SOP......... something that is trained, expected, maybe even on a checklist or written down. Something that is trained from one operator to the next.

How about such instructions are printed in all sorts of EMD service publications?

Hi.  It's me.  Let me see if I get this straight.

The whole point of blowing out the engine is to prevent damage coming from trying to compress any non-compressible fluids that somehow got into the cylinders.  This is usually due to leaks - which seem to be normal for these engines - and are more pronounced when the engines are broken in, well worn, and then cool off for a period (or are rarely run). By doing this, you prevent what could be a Very Bad Event happening.

But, this begs the next question: why does any owner/operator of these engines expect and/or accept a fluid leak? Isn't that sort of turning a blind eye towards something that needs attention?  If I see a leak under my F-350, it's gotta be tracked down before something costly happens.  Wouldn't the same thing apply here?  "A leak in Cylinder 6?  Let's report it and get it serviced before we're stuck with a blown engine!" Even if you do pump the fluid out, wouldn't there be a rust issue if that water sat too long, like in a museum situation?

I understand SOP - there are things I do every day that are "required" and you just tell yourself not to think about it and just do it.  Still, it seems odd that this falls under one of those rules.

"If I see a leak" is the loophole in your thinking. The practice prevents serious damage from the leak you didn't or couldn't see. Do you want the bent connecting rod to be how you found out about the internal leak?

Secondly, our SW-1 was built in 1940. How many 1940 Ford pickups have no leaks? I've been to a couple of car museums and can tell you they have pans or cardboard under all the exhibits, and they need them. When people get old, they often start leaking, too, and there's not much that can be done about it.

What has been missed in this discussion is that the EMD diesel is a TWO CYCLE engine. It does not have intake valves, it has intake ports around the circumference of the cylinder at the bottom of the stroke.

Those ports are open to the air box, where the intake air is pressurized by the Roots Blower and/or turbo charger. There are also water lines running through the air box. If one of those lines has a small leak, it would not be visible to anyone on a visual inspection of the engine. However, the water from that leak could run directly into any cylinder where the piston happens to be sitting at the bottom of its stroke. And that, my friends, is why you “blow down” an EMD diesel before you start it.

This is not some local railroad’s SOP. It is part of the standard starting procedure for every EMD 567 and 645 engine.

What has been missed in this discussion is that the EMD diesel is a two cycle engine. It does not have intake valves, it has intake ports around the circumference of the cylinder at the bottom of the stroke.

Those ports are open to the air box, where the intake air is pressurized by the Roots Blower and/or turbocharger. There are also water lines running through that air box. If there is a leak in one of those lines, the water can leak directly into any cylinder where the piston happens to be at the bottom of its stroke, uncovering those intake ports. A leak like this would not be visible on an external inspection of the engine. And that my friends, is why you “blow down” an EMD two-cycle diesel before you start it.

This is not a local railroad’s SOP. This is part of the standard starting procedure for every 567 and 645 EMD diesel engine.

@Rich Melvin posted:

What has been missed in this discussion is that the EMD diesel is a two cycle engine. It does not have intake valves, it has intake ports around the circumference of the cylinder at the bottom of the stroke.

Thanks for the facts on the engine design, but that opens a quick follow-up line of questions:

I realize the displacement is about a tenth of a standard EMD cylinder, but a Detroit Diesel 2-stroke, like those used in the older NYC bus fleet, never needed this special attention.  It, too, was Roots blown (none of ours ever had turbo units).  Was the difference in the design? That the Detroit water jacket didn't flow through the air handler unit, thus minimizing the chances of an internal leak that ended up filling the bore via the inlet ports?

Did the GE blocks, the 7FDL series, have the same design weakness?  I read that it's a 4-stroke, so it is safe to say that they never had this issue?

Thanks again for teaching an absolute novice about the way that real trains work!

Any reciprocating engine can have a hydraulic lock.  If you have a crack in the cylinder head of a Chevy 350 and the coolant leaks into the cylinder on the compression stroke you can bend a rod.  Two stroke or four.  As has been said, especially with an engine with removable cylinders there are lots of possible leaks.  I think GE engines had more leakage problems on the outside.  The EMD fuel lines are on the inside of the overhead, GE's connected separately to every cylinder. 

I'm not really sure why the DDs in buses or trucks never had the same procedure but it's just a different animal, cast iron heads and block, etc.  Not separate parts.  The cooling passages are cast in not bolted on and sealed with o rings.

The smaller 2-cycle Detroits (the 53, 71, 92 and 149 series) were a different design than the larger 567 and 645 engines. As you stated, they didn’t have any water lines in the air box, so no opportunity for a leak there. Incidentally, those numbers (53, 71, 92, etc.) are also the number of cubic inches per cylinder…so they did have that in common with their big brothers. Their model numbers were very easy to decipher, too.  An 8V92 was a V8 with 92 cubic inches per cylinder, for a total of 736 cubic inches.

The GE engines were 4-cycle, so they did not have any open intake ports in the cylinder sleeve.

I was an engineer for Santa Fe/bnsf, and can only remember a few times where I took time to blow out an engine before starting, and I can't recall ever blowing out a GE engine. I worked a few jobs with weekends off, and shut the engine down, so maybe on a monday morning, or if it was a fresh engine we didn't know, or hadn't used before. But never bothered with it if we used the same engine every day. Just fired it up and go. I did work for a small tourist road for a while, and they would sit all week or maybe two, so we blew those out, they were all EMD's without "creepy crank". I never came across any "known leakers" that actually squirted out anything other than a mist. Back to Caterpillar, The pony motor shares the same cooling system as the big engine, but also it's exhaust pipe runs through the big engine's intake manifold, warming the intake air pretty quickly.

Purging the cylinders was a once-a-day thing. Shutting down for a couple of hours did not require any further purging.

If you started and EMD engine after sitting for a couple of days without purging the cylinders ano had no damage, you got lucky.

Am I correct in saying that after a few days of sitting, the purge is recommended for both 2 cycle EMD’s and other 4 cycle diesels as well? Is one type of engine more prone to leakage into the cylinders than the other?

Only TWO CYCLE EMDs need to be purged.

Four cycle engines do not have open intake ports in the cylinder walls. They have intake valves in the cylinder head. Big difference.

This is a TWO CYCLE EMD power assembly (cylinder) showing the open intake ports in the cylinder wall. A four cycle engine does not have these ports.

@Rich Melvin posted:

Purging the cylinders was a once-a-day thing. Shutting down for a couple of hours did not require any further purging.

If you started and EMD engine after sitting for a couple of days without purging the cylinders ano had no damage, you got lucky.

Rich,
You didn't operate in the real world. Purging didn't happen and was never required. I can't imagine having to go open every cylinder cock, crank the engine over, go back and close all of the cocks then start the engine. On a five unit consist? NOPE! Didn't happen! Besides, a pipe wrench was not a tool in the tool box! The only time that I ever saw the cylinder cocks open was inside the roundhouse and I forget why we did it that day.

@Big Jim posted:

Rich,
You didn't operate in the real world. Purging didn't happen and was never required. I can't imagine having to go open every cylinder cock, crank the engine over, go back and close all of the cocks then start the engine. On a five unit consist? NOPE! Didn't happen! Besides, a pipe wrench was not a tool in the tool box! The only time that I ever saw the cylinder cocks open was inside the roundhouse and I forget why we did it that day.

Maybe the policy/procedure was different on the N&W/NS.  

@Rich Melvin posted:

Only TWO CYCLE EMDs need to be purged.

C'mon Rich,
You know better than that!

@Hot Water posted:

Maybe the policy/procedure was different on the N&W/NS.  

I doubt it!

@Big Jim posted:

I doubt it!

Well, doubt all you want but, was since I was on most of the class one railroads during my EMD career, starting with the N&W in 1962, and many, MANY railroads did indeed have a policy pertaining to "blowing out" the engine after so many hours of shut-down. Some railroads did and some railroads didn't.

@Big Jim posted:

Rich,
You didn't operate in the real world. Purging didn't happen and was never required. I can't imagine having to go open every cylinder cock, crank the engine over, go back and close all of the cocks then start the engine. On a five unit consist? NOPE! Didn't happen! Besides, a pipe wrench was not a tool in the tool box! The only time that I ever saw the cylinder cocks open was inside the roundhouse and I forget why we did it that day.

In the world I operated in on the Ohio Central, we were required to do this any time an engine was shut down for more than 48 hours. A pipe wrench was not needed. The purging valves had handles.

@Big Jim posted:

C'mon Rich,
You know better than that!

I should have explained better. In the context of only EMD and GE diesel locomotive engines, my statement would be correct.

@Rich Melvin posted:

A pipe wrench was not needed. The purging valves had handles.

Rich,
Like the photo linked, our engines (EMD Engine) didn't have handles. And, I don't remember any foreign engines having them either. I do remember the tell-tale marks of the trusty pipe wrench on them.

@Big Jim posted:

Rich,
Like the photo linked, our engines (EMD Engine) didn't have handles. And, I don't remember any foreign engines having them either. I do remember the tell-tale marks of the trusty pipe wrench on them.

Quite a number of railroads purchased those "after market" cylinder test valve inserts with the added-on "S handle" welded to the top. Besides, channel-lock pliers tended to work better than a pipe wrench, was fairly to heavy to carry. I always had the small EMD Service Toll with the 2 prongs, designed to fit the 2 holes in the top of the test valve stem. Besides, the test valve was NOT supposed to be tightened so darned tight anyway, as would have been done with a pipe wrench.

@Hot Water posted:

Well, doubt all you want but, was since I was on most of the class one railroads during my EMD career, starting with the N&W in 1962, and many, MANY railroads did indeed have a policy pertaining to "blowing out" the engine after so many hours of shut-down. Some railroads did and some railroads didn't.

Yeah, well as so many say, "I guess that there is a prototype for everything".  Yet it seems like from reading above that the SF/BNSF didn't require it and photos show that the CP didn't have any handles on their engines. Again, throughout my entire 40+ years (and before because they were like that when I got there), purging engines was never a requirement!

@Hot Water posted:

Quite a number of railroads purchased those "after market" cylinder test valve inserts with the added-on "S handle" welded to the top. Besides, channel-lock pliers tended to work better than a pipe wrench, was fairly to heavy to carry. I always had the small EMD Service Toll with the 2 prongs, designed to fit the 2 holes in the top of the test valve stem. Besides, the test valve was NOT supposed to be tightened so darned tight anyway, as would have been done with a pipe wrench.

Pipe wrench/Channel Locks, tomaytoes/tomahtoes!

This isn't exactly an answer to the first post, but i't about the test valve on an EMD.

My friend David Cassidy was walking through the engine room of an F45 which had settled down at 18 MPH in Run 8, while ascending the 2.2% Cajon Pass grade, and had just walked past the engine when a test cock blew out and hit the carbody so hard that it put a sizable outward dent in it.  Exhaust came pouring out and the noise and smoke was frightening.  He was between the cab and the engine, and so he quickly exited the engine room and shut down the engine.

If he had been right there when it happened, he would have been injured severely, as well as burned.  I never heard of this happening before or since, but I did see the engine with the big dent in the side panel.

Tom,
We had an engineer walk down the running board while lugging up the mountain when a whole power assembly exploded blowing the carbody door open right after he passed by! I've seen the aftermath of a few of these happenings and it is a total oily mess!!!

Back in the day (Hah) when I was an engineer trainee at the LIRR, we were trained to start the new EMD GP38s and other EMD locos that were new then. We were also trained on the outgoing ALCO equipment that required resetting the rack to start. On EMD I remember to this day the sequence at the door where the control was: an electrical box attached to the engine, with a panel containing a switch that moved left and right under spring tension. To the left- "FUEL Prime", to the right- "ENGINE START". Move the switch handle left until the fuel prime sounded that it was not airbound, and then to the right to start the Creepy Crank part of the fire-up procedure. After a few slow turns, the engine would spin faster and (hopefully) start. I never got blew up so I guess all worked as intended.

I was down at the WWRR today and confirmed with the recently retired Chief Mechanical Officer, who was serving as locomotive engineer, that a valve must be opened on each cylinder, three on each side of the locomotive (V6 SW-1) and that no wrench is used to loosen or tighten.

@Ken Wing posted:

I was down at the WWRR today and confirmed with the recently retired Chief Mechanical Officer, who was serving as locomotive engineer, that a valve must be opened on each cylinder, three on each side of the locomotive (V6 SW-1) and that no wrench is used to loosen or tighten.

OK then, what "tool" do they use to open and tighten those test valves? you sure can't do it by hand.