Fails to what?

Dave Faust

One of my current projects involves a steam-to-water heat exchanger, shell & tube style. It makes hot water for a heating airhandler. The steam is fed through a 1/3,2/3 set of pneumaticly controlled valves with a bypass line. The prints & the manufactures identification tag on both valves say they are normaly open valves. The valve stem on the larger valve can be seen moving downward when 20# air pressure is put on the operator. It comes back up when the controll pressure returns to atmospheric. The smaller valve seems to operate normaly, but tonight it's supposed to get too cold to use just the smaller valve by itself. With only the larger valve in service this unit makes 224 degree hot water (60 degrees outside) when the controll line is conected to the operator. The system cools off when the controll air line is disconected. With both valves in service water temperature is a reasonable 130 degrees when the outdoor air is 40 degrees. I expect trouble again when it warms up outside. What am I missing? Why does it get so hot? WAG's (Wild **** Guesses) tolerated. Anybody? (The valve was not manufactured after 1968, it's an oldie).

Dave Faust

Food for thought.

I just read Bill Nyes post on old equipment.
If my bosses could just hear this.

Dave Faust

Food for thought.

I just read Bill Nyes post on antiquated equipment in 'Heating Mind Set'.
If my bosses could just hear this.

Ray M

Valves

The valves should be normaly open(fail open) but according to your statement the water cools off with the line removed? sounds like you have one open and one closed.


Ray m

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

thp_8

What your not

seeing is the spring ranges of the two valves or the pneumatic controller that is running these two steam valves is out of adjustment. On most pneumatic systems a good controls person could have this back in tune in minutes. The valves should as they are 1/3 2/3 throttle the load. P.S. in the pneumatics world 1968 is not old. Pneumatics are built to last.

Al K._2

Valves

The 1/3-2/3 valves are normally sequenced to open the smaller valve first, then the larger, for accurate control of the HX.

The valves might be N.O., but with reverse-acting actuators which would fail to no heat. Most HX's I've worked with are set up this way to prevent runaway conditions should the pneumatics fail for one reason or another.

Thanks,
Al K.