15 feet per second

J. R. Sullivan H&P

Hi All,

  I know from reading "The Lost Art of Steam Heating" that 15ft/sec. is said to be the maximum exit velocity for dry steam. However, my gas fired steam boiler (160,000 BTUH input) with two 2" risers into a 2" header has a calculated exit velocity of just under 24ft/sec. The pressuretrol is at 1 1/2 psi. This system has operated quietly and without surging for over 10 years. So I wonder: is 15 ft/sec. the actual top speed for not dragging  water from the boiler or was an engineer just being conservative?   

Steamhead

Not sure which

and is this a Utica or Columbia boiler?

Hap_Hazzard

Is that based on the total output?

If it is that would mean 12 ft/sec per riser. If your risers are > 24" of vertical above the maximum water level, the droplets should fall back at < 15 ft/sec. I think 15 ft/sec is the minimum velocity for entrainment.

STEAM DOCTOR

Exit speed

In this application,assuming 82% efficiency and 0psi(thats when the steam is the fastest), the exit speed through one 2" riser would have been approximately 44 feet per second. With two 2" risers, the speed through each riser is approximately 22 feet per second. 22 feet per second is certainly better than the bulk of steam installs and in my book would be totally acceptable. If you are not having any issues then I would definitely leave it as is.

STEAM DOCTOR

Header

The issue that you may have would be with the the somewhat undersized header. The steam will increase speed when it hits the header. That,in turn, could cause an increase in speed through the risers. However,if your risers have adequate rise and if you are not having issues , then I would sleep easy.