1/4” and 3/8” Tap capacity??

cnjamros

Has anyone calculated the venting capacity of 1/4” and 3/8” tappings in a main? I see 1/8” and 1/2” on the venting capacity chart, but my system has tappings are in between and I would like to know how much i can get out of the existing taps.

Pumpguy

I have orifice flow charts compiled by The Nash Engineering Company in the late 1930s. These were used primarily for volume capacity performance testing their vacuum pumps and compressors.

The approximate hole size for 1/4" and 3/8" NPT tappings are 7/16" and 9/16".

These tables show that discharging 60 degree F. air @ one PSIG, the flow through a 7/16" orifice is 13.7 ACFM. The flow through a 9/16" orifice is 22.4 ACFM.

Unfortunately, these flow tables don't show anything below one PSI.

Additional searching using an online flow calculator shows that discharging 120 degree F. air @ 0.25 PSIG through a 7/16" orifice has a flow rate of 7.3 SCFM. Through a 9/16" orifice, the flow is 11.8 SCFM.

Hope this information is of some use.

JUGHNE

Are the existing taps you have into a Tee?
It was rare for a tee of steam pipe sizes to have less than 1/2" branch.
Do you have bushings in your tees?

Gsmith

Very generally the venting capacity will be proportional to the square of the hole diameter, so, again very generally, a 1/4" hole is 4 times the area of a 1/8" hole and so should vent at about 4 times the capacity; a 3/8" hole is 9 times the area of a 1/8" hole and should vent at 9 times the capacity; to double check it from the 1/2" vent chart a 1/4" hole is 0.5 the diameter of a 1/2" hole and thus 25% of the area of a 1/2" hole and so should vent at 25% (0.5 squared) of the capacity of a 1/2" hole; and a 3/8" hole is 75% of the diameter of a 1/2" hole and so should vent at about 56% of the capacity of a 1/2" hole (0.75 squared).

JUGHNE

Bushings??

cnjamros

There are no bushings in these taps... each one currently feeds into a reducing elbow (reversed) that upsizes to 1/2" for my Gorton #2s.

JUGHNE

Any pictures of that?