www.fueloilnews.com | FUEL OIL NEWS | FEBRUARY 2015 43
HVAC/ HydroniCs
which senses the steam, is only about 25% of the surface area
of the diaphragm of a vapor control. Keep in mind you are
working with a vapor.
3) Vapor controls, L408J, Figure 2, operate on ounces,
and can be purchased in maximum operating pressures of
just 1 psi (16 ounces). The idea is to stay under 1-1/2 pounds
and these controls do that.
4) Most, if not all, residential steam systems ever designed
were laid out for an operating maximum pressure of two
psi.
5) Any control, regardless of price, is cheaper than repeat
calls.
This is a common problem, and so I have to keep wonder-
ing when everybody will stop putting on the wrong controls
and put on the right ones? Don't think that all you have to
do is up the capacity of the air vents either. If you do, you
will probably create even bigger problems. What problems
you ask? Well, how about problems with "water hammer,"
condensate return and if an automatic feeder is present,
flooding of the boiler. Take the easy way out—put on a vapor
control.
Basic steam rules regarding pressure boils down to this.
If the radiators don't heat, make sure they're not over pres-
surized. Make sure they are in "radiator level," pitched back
to the inlet and if they still don't heat, change or adjust the
vent valve. If that doesn't do it you need to look at piping
and now you need a long course in steam. If you go out look-
ing for L408 controls you will also find another change, no
more mercury. The L408A has been replaced with the L408J,
Figure 2, just in case you were interested.
The proper level of water in a steam boiler is also essential
for correct and safe operation. The most common of the
water controls is the low-water cutoff. In addition, there are
water feeders, pump controllers and combinations of low
water cutoff/feeders, and low water cutoff/pump controllers.
Let's start with the easiest one first, and work our way up.
The low water cutoff shown in, Figure 3, is a float-type
cutoff. The model shown is the last of its type made. The #67
from McDonnell & Miller has been in use for many years
and serves its purpose. It once had many competitors from
companies such as Watts, Econo and Honeywell, but these
products are no more.
The #67 works with a simple float attached through a bel-
Figure 2
Figure 3
