SHAKING and BUCKING Pipes
SHAKING and BUCKING Pipes
Question from Gary, a design engineer: Will an Oiler's controller automatically reduce the fuel flow rate when it senses the Receiving Ship's valves gradually throttling closed.
This dialoge has facilitated informal background research, between Raytheon engineering designing Zumwalt DDG-1000 machinery systems, and former Navy Crewman. At issue are the consequences of potentially introducing automation to the FAS UNREP design on the receiving Ship, which is not traditionally done, but is worthy of discussion and debate. September 7, 2009
There are so many variables here.
Back when "we" were doing it, there was zero automation. Unfortunately there was also almost no understanding of the laws of physics as well, especially on the receiving ships.
The tendency was to equate pressure with flow rate (the prevailing thinking being "If I see a higher pressure on the gauge on the fuel riser, that tells me that the fuel is flowing in at a higher rate." So higher pressure equals more fuel being delivered)
In truth, pressure results from resistance to flow - so "pressure" as seen on a gauge can come from a variety of sources. One source of "pressure" is that the fuel is indeed flowing so rapidly that it is approaching the delivery capacity of the plumbing system and this is causing the pressure rise (in this case the supposition is correct that a higher pressure reading is indeed being caused by a high delivery rate and everyone is happy).
Another source of a high pressure reading is a closed or partially closed valve on the receiving ship. The "pressure" is still high, but the rate of fuel being delivered is low or even zero.
In some cases, the receiving ship had amply sized piping and all the valves were wide open - the pressure on the deck riser was fairly low but we were pumping a terrific volume of fuel and their tanks were filling rapidly, but the guy on the high-line sound powered phone would still be screaming for "MORE PRESSURE"
Everyone (and I do mean everyone!) wanted to know how many gallons per minute for a given "pressure" on the deck riser gauge. There was absolutely no relationship between the "pressure" and the volume, but I could never seem to explain this, so, in the end I gave up.
So, at long last, the answer to your question. I suspect that when the FAS gear on the oiler senses increasing "PRESSURE" AND decreasing volume it will automatically reduce the delivery rate. Assuming that the cargo pumps are centrifugal (as opposed to some sort of fixed volume pumps such as piston or screw pumps), this would happen in any event, as increased pressure (pressure = resistance or opposition to flow) will result in reduced delivery rate.
I do remember, particularly in Pearl Harbor at the fuel pier when we were taking on fuel and were about to get full and stop delivery we had to plan several minutes in advance and very gradually close off our inlet valves. The fuel farm tanks were up on a RED HILL overlooking the harbor a couple of miles away. Once all that fuel got moving through the miles of pipe it developed quite a bit of momentum, and as we closed off the valves on the ship it was like stopping a freight train - the pressure increased dramatically as the fuel kept trying to move ahead through the pipe, which would stark bucking and shaking on the dock. It was all quite dramatic.
Those were the days! Best wishes, Harris, Liquid Cargo Officer 1975-78
One crew member says, "It's much like a garden hose, leave the nozzle off and flow goes up pressure goes down, put on a nozzle and pressure goes up and flow goes down." Sam Hobbs - MM3 1965-67
Another crew member says, "The liquid cargo pumps on Kawishiwi were indeed centrifugal, but they were steam driven - hence variable speed. System heads also varied with different tank levels and hose configurations. So while a centrifugal pump has a fixed pressure performance curve for each speed and head, functionally there was no relation between delivery & pressure (as the system curve & speed were not given). Operators could roughly sense flow rate by the hum in the lines. But as long as the pressure was not excessive, we weren't too concerned, as long as everything looked OK on deck or as reported over the station phones.
I recall that the cargo pumps had flow meters - differential pressure gauges scaled in GPM - installed across across fixed orifice plates in the discharge line. This would, under all conditions, tell the pumproom operators roughly the delivery rate at each pump. Provided the gages worked."Jon Bernard - B & M Division Officer 1970-72
Not included in Lary's attempt to define the operation above is what Lary did after he was asked what the gallons per minute was at a given pressure. Instead of explaining that there was no difference, Lary simply made up a totally bogus spreadsheet that showed how many gallons per minute the ship was receiving for a given pressure reading on the deck riser. He xeroxed about a zillion copies of this and sent one over on the high line to every customer ship. Knowing Lary, everyone loved this thing and he became a local celebrity even though it was a totally spurious document! One could say that a good officer would not put out such a report, it could cause some unsuspecting fool to use his data & get some folks hurt, but again they knew the source of the report, the report would not fit the current unrep operation, and they needed a good laugh so the report would not be kept. Webmaster
I guess I'm missing the point on how this could have "hurt" anyone. Gee Wiz! Maybe if they rolled it up real real tight and poked themselves in the eye with it? Lary
Thanks for the reply Lary.
A totally bogus spreadsheet that showed how many gallons, That's hilarious! I believe it.
When you say "automatically reduce", do you mean without human intervention of any kind.
I'm very hesitant to believe that gradual closure (be it manually or automatically triggered) of Receiving-Ship Tank's Inlet Valves will "automatically" indirectly result in any gradual reduction in pressure, or flow rate (volume, GPM, whatever we want to call it) on the part of the Oiler. I think manual intervention on the Oiler always plays a role.
This is just the way Oilers work.
That's why it's a waste of resources to automatically close tank-by-tank inlet valves on the Receiving ship. The Receiving ship crewman still has to monitor their tank levels, and communicate to the Oiler that volume must be decreased, so there's just no benefit to automating the Receiving ship valves. Gary, a design engineer.
Now everyone has these walkie talkies. It is getting full and the people up on the hill shut it down. No more jumpping pipes. Love the modern conveniances. They will never know what jumping pipes even look like. These stories are priceless. Lea Burris ET1 (SW) 1990-1992
On the pressure issue; when I was pumping from HASS to an empty AOR/AOE with tanks and valves open wide, I don't recall going above 40 psi on my side. They were practically siphoning it on their side and I was moving prodigious amounts of fuel; 3 main fuel pumps, wide open from full tanks.
Working with the shooters, their piping wasn't large enough to take all we had to offer. I'd give a DD/FF a full load every 2-3 days in about 42 minutes with one rig (yes, 42 minutes was fleet average- I did a lot of them).
Once the MSC oilers appeared in the Far East it took a while to get the USN to trust us, but they found that when they asked us to pump full we would, when they wanted less pressure we would and when we got the countdown for stop pumping, we would. We in turn trained them not to squeeze down on us with their valves. If they did, it messed up the top off, sometimes burst hoses and heaven forbid, put oil in the water.
The normal operation for a tin can was to sink the probe, start pumping at 40 psi (minimum pressure), work up to 100 psi, at about 10 minute standby drop to 50/60 psi, at 5 minutes drop to 40 psi, then do a minute by minute countdown to stop pumping. The most gallons I remember pumping is 1,800 gallons per minute to a smaller ship at the lower psi.. We had them keep the valves open to their tanks and we would reopen our valves and take a back suction by draining the fuel in the hoses (this was a suction) back into our tanks. That would flatten the hose, not take any fuel from them, and make breakaway a tidier event.
Under no circumstances would I take the human element out of the unrep operation. If you don't do it all the time it is not an easy evolution to master. In the Far East we could make 7th Fleet look good because we did it all the time. On KAWISHIWI in San Diego, she always looked good because she did so much with FLETRAGROUP, but new commissions and ships out of overhaul were horrible.
Anyway, if you have dueling automated systems trying to outguess each other there is going to be an oil spill.
I have been in one of the Red Hill fuel tanks. 1983 I was master on either CHATTAHOOCHEE or TALUGA in Pearl and talked my way into an inspection of a tank under maintenance. I felt like an ant in a refrigerator.All the best, Pat Moloney; past Master of Kawishiwi
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