Two-Pipe Vacuum System - an ordinary two pipe vacuum system uses a vacuum
pump to create a sub atmospheric pressure, usually 3" to 8" Hg (Mercury), in the
return piping. Vacuum removes air from system piping and heat emitters to provide
quick heating and efficient steam distribution. Condensate flows to the pump receiver
by gravity.
Up-Feed System - Steam system for multiple floor buildings in which the steam
supply main is in the basement above the boiler. Risers carry steam to the heating
units. Condensate from each up-feed riser is dripped by gravity into wet return and
then flows via Hartford Loop to the boiler. The supply main is kept free of condensate
accumulation for free flow of steam.
Vacuum Heating System (Steam) - a one or two pipe heating system equipped
with the necessary accessories to allow the pressure in the system to go below
atmospheric. A closed heating system in which a partial vacuum is induced when
the heating units and the main cool below the boiling point of water at atmospheric
pressure. Pressures in a vacuum system range from below atmospheric pressure
to a higher pre-determined pressure. Space heating is more even, and boiler water
temperatures are usually lower; heating is more economical. Vacuum vent valves and
vacuum main vents must be used.
Vacuum Pump Equalizer - a piping arrangement that equalizes induced vacuum
between the supply header and vacuum pump receiver.
Vapor Stat - a device that provides an operating control and high limit protection
for vapor heating systems with pressures up to 4 psi (8 kPa). All models have
Microswitch snap switches to open or close a circuit on a pressure rise.
Vent Valve (heat emitter) - a device which opens to allow air to be pushed out
of a pipe or a heat emitter but which closes against water. Installed on a tapping at
the opposite end of the heat emitter from the supply valve, float and thermostatic
vent valves let air escape from the heating unit under pressure, but close against the
passage of steam and condensate.
Water Hammer - a wave transmitted through a pipe filled, or partially filled, with
water. It may originate as waves set up by steam passing at a high velocity over
condensate collected in piping. It is one of the main causes of noise in steam heating
systems and is the cause of much damage to thermostats and floats in traps.
Wet Return - the part of the return main that is below the boiler water line and filled
with water (does not carry air or steam).
National Oilheat Research Alliance 57