Hydraulic Back Pressure Valve : Cyl Knife Gate Valves.
Hydraulic Back Pressure Valve
Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow.
Pressure that resists the flow of fluid in a piping system.
Pressure which creates resistance against a flow of water.
Denoting, relating to, or operated by a liquid moving in a confined space under pressure
(of cement) Hardening under water
Of or relating to the science of hydraulics
moved or operated or effected by liquid (water or oil); "hydraulic erosion"; "hydraulic brakes"
of or relating to the study of hydraulics; "hydraulic engineer"
(hydraulics) fluid mechanics: study of the mechanics of fluids
A cylindrical mechanism in a brass instrument that, when depressed or turned, admits air into different sections of tubing and so extends the range of available notes
A device for controlling the passage of fluid through a pipe or duct, esp. an automatic device allowing movement in one direction only
device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone
A membranous fold in a hollow organ or tubular structure, such as a blood vessel or the digestive tract, that maintains the flow of the contents in one direction by closing in response to any pressure from reverse flow
a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it
control consisting of a mechanical device for controlling the flow of a fluid
A-6E Intruder Partial Ejection, trap
Lieutenant Keith Gallagher's Account of the Incident
Murphy's Law says, "Whatever can go wrong, will, and when you least expect it." (And, of course, we all know that Murphy was an aviator.) Murphy was correct beyond his wildest dreams in my case. Fortunately for me, however, he failed to follow through. On my 26th birthday I was blindsided by a piece of bad luck the size of Texas that should have killed me. Luckily, it was followed immediately by a whole slew of miracles that allowed me to be around for my 27th. Not even Murphy could have conceived of such a bizarre accident (many people still find it hard to believe), and the fact that I am here to write about it makes it that much more bizarre.
We were the overhead tanker, one third of the way through cruise, making circles in the sky. Although the tanker pattern can be pretty boring midway through the cycle, we were alert and maintaining a good lookout doctrine because our airwing had a midair less than a week before, and we did not want to repeat. We felt we were ready for "any" emergency: fire lights, hydraulic failures and fuel transfer problems. Bring 'em on! We were ready for them. After all, how much trouble can two JO's get in overhead the ship?
After my third fuel update call, we decided that the left outboard drop was going to require a little help in order to transfer. NATOPS recommends applying positive and negative G to force the valve open. As the pilot pulled the stick back I wondered how many times we would have to porpoise the nose of the plane before the valve opened. As he moved the stick forward, I felt the familiar sensation of negative "G", and then something strange happened: my head touched the canopy. For a brief moment I thought that I had failed to tighten my lap belts, but I knew that wasn’t true. Before I could complete that thought, there was a loud bang, followed by wind, noise, disorientation and more wind, wind, wind. Confusion reigned in my mind as I was forced back against my seat, head against the headrest, arms out behind me, the wind roaring in my head, pounding against my body.
"Did the canopy blow off? Did I eject? Did my windscreen implode?" All of these questions occurred to me amidst the pandemonium in my mind and over my body. These questions were quickly answered, and replaced by a thousand more, as I looked down and saw a sight that I will never forget: the top of the canopy, close enough to touch, and through the canopy I could see the top of my pilot's helmet. It took a few moments for this image to sink into my suddenly overloaded brain. This was worse than I ever could have imagined - I was sitting on top of a flying A-6!
Pain, confusion, panic, fear and denial surged through my brain and body as a new development occurred to me: I couldn't breathe. My helmet and mask had ripped off my head, and without them, the full force of the wind was hitting me square in the face. It was like trying to drink through a fire hose. I couldn't seem to get a breath of air amidst the wind. My arms were dragging along behind me until I managed to pull both of them into my chest and hold them there. I tried to think for a second as I continued my attempts to breathe.
For some reason, it never occurred to me that my pilot would be trying to land. I just never thought about it. I finally decided that the only thing that I could do was eject. (What else could I do?) I grabbed the lower handle with both hands and pulled-it wouldn't budge. With a little more panic induced strength I tried again, but to no avail. The handle was not going to move. I attempted to reach the upper handle but the wind prevented me from getting a hand on it. As a matter of fact, all that I could do was hold my arms into my chest. If either of them slid out into the wind stream, they immediately flailed out behind me, and that was definitely not good.
The wind had become physically and emotionally overwhelming. It pounded against my face and body like a huge wall of water that wouldn't stop. The roaring in my ears confused me, the pressure in my mouth prevented me from breathing, and the pounding on my eyes kept me from seeing. Time had lost all meaning. For all I knew, I could have been sitting there for seconds or for hours. I was suffocating, and I couldn't seem to get a breath. I wish I could say that my last thoughts were of my wife, but as I felt myself blacking out, all I said was, "I don't want to die."
Someone turned on the lights and I had a funny view of the front end of an A-6, with jagged plexiglas where my half of the canopy was supposed to be. Looking down from the top of the jet, I was surprised to find the plane stopped on the flight deck with about 100 people looking up at me. (I guess I was surprised because I had expected to see the pearly gates and some dead relatives.) My first thought was that we had never taken off, that something had happened before the catapult. Then eve
Eiffel Tower guts
Passenger lifts
The Eiffel Tower, October 2007
[edit]Ground to the second level
The original lifts to the first and second floors were provided by two companies. Both companies had to overcome many technical obstacles as neither company (or indeed any company) had experience with installing lifts climbing to such heights with large loads. The slanting tracks with changing angles further complicated the problems. The East and West lifts were supplied by the French company Roux Combaluzier Lepape, using hydraulically powered chains and rollers. Contemporary engravings of the lift cars show that the passengers were seated at this time but it is not clear whether this was conceptual. It would be unnecessary to seat passengers for a journey of a couple of minutes. The North and South lifts were provided by the American Otis company using car designs similar to the original installation but using an improved hydraulic and cable scheme. The French lifts had a very poor performance and were replaced with the current installations in 1897 (West Pillar) and 1899 (East Pillar) by Fives-Lille using an improved hydraulic and rope scheme. Both of the original installations operated broadly on the principle of the Fives-Lille lifts.[34][35]
The Fives-Lille lifts from ground level to the first and second levels are operated by cables and pulleys driven by massive water-powered pistons. The hydraulic scheme was somewhat unusual for the time in that it included three large counterweights of 200 tonnes each sitting on top of hydraulic rams which doubled up as accumulators for the water. As the lifts ascend the inclined arc of the pillars, the angle of ascent changes. The two lift cabs are kept more or less level and indeed are level at the landings. The cab floors do take on a slight angle at times between landings.
The Eiffel Tower illuminated in blue to celebrate the French presidency of the EU (July 2008)
The principle behind the lifts is similar to the operation of a block and tackle but in reverse. Two large hydraulic rams (over 1 metre diameter) with a 16 metre travel are mounted horizontally in the base of the pillar which pushes a carriage (the French word for it translates as chariot and this term will be used henceforth to distinguish it from the lift carriage) with 16 large triple sheaves mounted on it. There are 14 similar sheaves mounted statically. Six wire ropes are rove back and forth between the sheaves such that each rope passes between the 2 sets of sheaves 7 times. The ropes then leave the final sheaves on the chariot and passes up through a series of guiding sheaves to above the second floor and then via a pair of triple sheaves back down to the lift carriage again passing guiding sheaves.
This arrangement means that the lift carriage, complete with its cars and passengers, travels 8 times the distance that the rams move the chariot, the 128 metres from the ground to the second floor. The force exerted by the rams also has to be 8 times the total weight of the lift carriage, cars and passengers, plus extra to account for various losses such as friction. The hydraulic fluid was water, normally stored in three accumulators, complete with counterbalance weights. To make the lift ascend, water was pumped using an electrically driven pump from the accumulators to the two rams. Since the counterbalance weights provided much of the pressure required, the pump only had to provide the extra effort. For the descent, it was only necessary to allow the water to flow back to the accumulators using a control valve. The lifts were operated by an operator perched precariously underneath the lift cars. His position (with a dummy operator) can still be seen on the lifts today.
The Fives-Lille lifts were completely upgraded in 1986 to meet modern safety requirements and to make the lifts easier to operate. A new computer controlled system was installed which completely automated the operation. One of the three counterbalances was taken out of use, and the cars were replaced with a more modern and lighter structure. Most importantly, the main driving force was removed from the original water pump such that the water hydraulic system provided only a counterbalancing function. The main driving force was transferred to a 320 kW electrically driven oil hydraulic pump which drives a pair of hydraulic motors on the chariot itself thus providing the motive power. The new lift cars complete with their carriage and a full 92 passenger load weigh 22 tonnes.
A view from above
Due to elasticity in the ropes and the time taken to get the cars level with the landings, each lift in normal service takes an average of 8 minutes and 50 seconds to do the round trip spending an average of 1 minute and 15 seconds at each floor. The average journey time between floors is just 1 minute.
The original Otis lifts in the North and South pillars in their turn proved inferior to the new (in 1899) French lifts and were scrapped from the south pilla