Wastewater Conveyance - Wastewater Operators - page 222

figure 4.47 Air receiver.
functions provided by an air receiver for an air system. That is, the accu-
mulator (usually a dome-shaped or cylindrical chamber or tank attached
to a hydraulic line) in a hydraulic system works to help store and deliver
energy as required. Moreover, accumulators work to help keep pressure
in the line smoothed out. If, for example, pressure in the line rises sud-
denly, the accumulator absorbs the rise, preventing shock to the piping. If
pressure in the line drops, the accumulator acts to bring it up to normal.
Note: The primary function of an accumulator in a hydraulic system is
to supplement pump flow.
4.15.6 air receivers
As shown in Figure 4.47, an air receiver is a tank or cylindrical type of
vessel used for a number of purposes. Most important is their ability to
store compressed air. Much like accumulators, they cushion shock from
sudden pressure rises in an airline. In this way, the air receiver serves to
absorb the shock of valve closure and load starts, stops, and reversals.
There is no liquid in an air receiver. The air compresses as pressure rises.
As pressure drops, the air expands to maintain pressure in the line.
Note: OSHA has a standard, 29 CFR 1910.169(a), requiring that air receiv-
ers be drained. Specifically, the standard states, “A drain pipe and valve
shall be installed at the lowest point of every air receiver to provide
for the removal of accumulated oil and water” (OSHA 1978). This is an
item that should be taken seriously, not only for safety reasons but also
because it is a compliance item that OSHA inspectors often check.
4.15.7 heat exchangers
Operating on the principle that heat flows from a warmer body to
a cooler one, heat exchangers are devices used for adding or remov-
ing heat and cold from a liquid or gas. The purpose may be to cool one
body or to warm the other; nonetheless, whether used to warm or to
cool, the principle remains the same. Various designs are used in heat
exchangers. The simplest form consists of a tube or possibly a large coil
of tubing placed inside a larger cylinder. In an oil lubrication system,
the purpose of a heat exchanger is to cool the hot oil; however, a heat
exchanger system can also be used to heat up a process fluid circulat-
ing through part of the heat exchanger while steam circulates through
its other section.