I've got an old 20 gal (?) compressor tank in which I want to install a
drain. I'm guessing it to be 1/4-inch (6.3 mm?) thick steel. Tank is rated to
125 psi.
Can I drill and tap this for 1/4 or 3/8-inch pipe? Or should i get a "plug"
welded to it that I can drill & tap?
Are there rules to follow for such stuff? Is there a better n.g. to ask this
question in?
Thanks,
I got a great find last year in a nice two-stage pump that only needed the
valves re-seated to make it cherry again. I was also given a beautiful,
hot-dip galvanized upright propane tank of 100gal capacity. Hmmmm..... I
think I see a picture here.
I didn't want to compromise the tank's integrity because I'm NOT a good
weldor. So, I looked at things from a Rube Goldberg point of view.
Here were: fill port, output port, and gauge port. The fill and output were
both 1" NPT bosses in good shape. The gauge port was a huge 2-1/4" machined
flange with the gauge bolted down onto a gasket.
Ok... fill will be fill; just screw in a check valve. Output was output;
natch. Took off the gauge and extracted the float assembly. Machined a
manifold that sat where the gauge used to.
In the manifold is a: Pressure relief port (tested... it does keep ahead of
the pump), a pressure gauge port, and... and... a dip-tube drain. It's just
a copper pipe that kisses the bottom of the tank, and a petcock valve to
open it to ambient pressure. Air pressure pushes the water up the tube.
I welded the pump base to the top flange and the feet to the bottom
flange -- never once touched a torch to the tank itself.
Since I'm not a weldor, I feel safer, and I've got a perfectly servicable
upright that has a drain valve I can actually reach without aggravating my
knees.
LLoyd
Thus spake Lloyd E. Sponenburgh:
This sounds like a very creative idea, but I'm having difficulty picturing
what your set-up is. (A compressor with a "float assembly"? Water actually
accumulates enough to require a float?)
I've got 2 ports on this tank: input (small boss fitted with 1/4 copper tube
connecting to compressor output), and output (large (2-inch?) threaded boss
with 1/4ntp threaded adapter (plug) connecting to 1/4 pipe with tees for
gauge and quick disconnect hose fitting).
Hmm... I could adapt the input to also act as output, and put the dip-tube
drain on the large boss.
How, exactly, is a dip-tube drain constructed? How do you fit a tube
internally and connect that to the backside of a 1/4ntp (or such) output?
I like the idea. It would fit in nicely with the large boss at the front of
the tank.
Thanks,
Thus spake DaveC:
What's the purpose of a pressure relief port? Is this an "open at x psi"
valve to keep pressure below the tank's limit? But this is what an electrical
pressure switch does.
What's a relief port?
It was a propane tank in real life. It had a float-actuated gauge. The
gauge port was BIG, so it was a nice place to combine some functions.
The manifold had two holes straight through into the top of the tank: one
for the relief valve and one for the new pressure gauge. It had a THIRD
hole that had a petcock on the outside, and a copper compression fitting on
the inside to accept the dip tube.
LLoyd
Dave, pressure switches weld shut in storms, or with age, or with mud-dauber
nests inside them.
EVERY compressor must have a pop-off valve to protect the tank from
over-pressure.
LLoyd
Thus spake Lloyd E. Sponenburgh:
So I guess without some custom "manifold" or such, there's no way to fit a
dip tube, internally. All I have is threaded holes in the tank for 1/4 inch
input, and 3/8 inch output (previous message said 1/4 output, which was an
error).
Ideas?
Thanks,
Thus spake Lloyd E. Sponenburgh:
Well, it looks like several things need to be added to this old compressor.
I looked closely and discovered a third port, down low on the end where the
handle attaches. It is a 3/4 inch (?) threaded boss with a square-head plug
threaded in. A 'manual' drain valve, I guess.
This old compressor has the basics, but needs some safety items. Drain valve
and pop-off valve to be added.
Thanks for your help,
That sounds very strange. I have an old Craftsman -- horizontal
tank, belt-driven pump, two wheels at one end and a handle at the other.
Between the wheels, on the underside, is the drain valve. It
was rather small -- perhaps 1/4" NPT thread. It had a T-handled valve,
which was hollow for the water to flow out. It was rather prone to jam,
so I replaced it with one with a knurled knob on the end, and a silicone
rubber-gasketed seat on a wider portion on the inside. That one remains
controllable with just my fingers.
If there were room, I would replace it with a timer controlled
solenoid valve, but there is not on this one.
You might consider looking up the parts list for your model on
Sears' website, to see whether it lists a drain valve as part of what it
should have.
I could imagine taking the output fitting and replacing it with
a concentric fitting, with the inner part being a dip tube to drain from
near the bottom, and the outer part passing air to the regulator.
Enjoy,
DoN.
Are there rules for such stuff? I would hope there are, in your country.
If you don't know the answer without asking don't mess with air or gas
filled pressure systems.
There are some very scary answers to this question.
You could try avoiding modifying the tank altogether. Get a pipe
cross, mount the tank above so the pipe has to go up to get into the
tank, then have a six to eight inch (assuming it's 3/4 or 1"--longer for
thinner pipes unless you don't mind draining more often) leg of pipe go
out the bottom of the cross to collect water and gunk. Stick a drain at
the bottom of that pipe. Then use the remaining two sides of the cross
for inlet and outlet.
Not pretty or very mobile, but works OK.
A welded iron half-coupling is the correct way to go. Do it yourself if
you can. Your tank isn't worth what a shop would have to charge--about
$80 or their one hour minimum.
good luck,
Boat_dreams
A 'Pressure relief port or valve' is a redundant safety feature. (Required
by most codes for any pressure vessel.) Electrical pressure switches do
fail.
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