An auditor recently received a call about low pressure from a client operating a printing plant. The main presses were having production issues and the plant pressure needed to be increased to compensate. Because the client had received a financial incentive for lowering his pressure, the power company was breathing down his neck to return the pressure to the original value or return the money.
The auditor dutifully went to investigate and placed data loggers at strategic points along the plant distribution network. The instruments indeed found excessive pressure differential, showing the presses were being starved for air. What was strange was that the presses were located only 20-ft away from the compressor room and had adequately sized distribution piping. The piping drops to the press were well sized for peak flows and so too were the filter/regulator/lubricators within the press. After very careful investigation there appeared to be no reason for the pressure differential, and yet there it was.
The auditor was stumped. He walked up and down the distribution system scratching his head and looking for the cause, until a slightly sheepish looking maintenance working tapped him on the shoulder. The worker had been involved in installing the distribution piping years ago and had installed two isolation ball valves at the source inside the compressor room. It turned out that the ball valve were installed too close together so the handles touched, meaning they both could not be fully opened at the same time. To fix the problem, he modified one of the handles so that when it was open the handle was at 90°, solving the problem. In the years that passed, he forgot about the valve and one day one of his co-workers “opened” what he thought was a closed valve. Because the valve was actually closed, instead of sending air directly to the presses, the air had to travel to the far end of the plant and back to feed the presses. He has suddenly remembered his modification and sure enough that was the problem.
Returning the valve to its open position solved the problem. The valve was quickly corrected by properly installing the valve with the correct handle. Problem solved!
Learn more about measuring pressure differential in the Compressed Air Challenge webinar scheduled for November 2013.
By Ron Marshall for the Compressed Air Challenge
Neil says
Excellent example of why things shouldn’t be done 1/2 way. Valve handles should never be turned, they’re universally accepted that handle direction shows off and on. What if this would have been a gas line in a different situation. BAD IDEAS! Good find (or dumb luck of remembering)
Bernie says
I’m not a genius in compressed air delivery but I did see something very interesting at a plant I worked at. They had a large screw compressor and drier for high volume air needs for machinery and painting. The piping installed around the plant actually circled the plant, there were no dead ends. All feeds went up before they dropped and the entire delivery piping was properly pitched and had a suitable number of drain drops. We were never starved for dry air anywhere in the plant.
Art Galvan says
Thats what happens when people do a half ass job.
Geoff Daly says
This is not unknown for two valves to be too close when using a short nipple to join, instead of an intermediate Dart-union. Then, the valves could be orientated off-set or just cut the handles shorter so they did not interfere and not reposition a handle or use a longer nipple.
Will Holding says
Bernie, that loop type setup you are referring to is called a “pressure balancing loop” and works very well- in plumbing, it is also used to balance the pressure drop between multiple body sprays in a shower.
There are a couple of “better” solutions to valve handle interference problem, and it sounds like this guy did not use any of them.
You can orient the valves so the handles are on the outside of the pipes, facing away from each other. Or you cann offset the valves one downstream of the other. Or you can cut the handle down, or better still mill a slot in a bit of bar stock to make a “T” handle, which swings in half the length of the level hande, still indicates valve position, and can be turned with as much torque as the lever handle, Or lastly and perhaps most simply, take the retainer nut off the handle and hang the handle near the valve on a wire from the pipe. This is an air line, so it’s an isolator valve, not an emergency shutoff.
William K. says
So what is the motivation for putting two valves in series like that? If you want a safety shutoff that is reliable, use a “ross” valve, which is made for that exact purpose, and no other. Not good looking but very effective, and OSHA approved. And when they are open there is very little pressure drop. Of course, in this case I would have done a flow-pressure drop test, since the symptom was low air pressure during flow. That would have discovered the problem.