Environmental Engineering Reference
In-Depth Information
Tubing
Control unit
Bulb
Valve body
Closing element
figure 4.36 Pressure-regulating valve system.
use, no more than 30 psi air is usually required (depending on required
usage, of course). The air is supplied by an air compressor, which nor-
mally operates long enough to fill an accumulator with pressurized air
at a set pressure level.
When shop air is required, for whatever reason, compressed air is
drawn from the connection point in the shop. The shop connection point
is usually connected via a pressure reducer (sets the pressure at the
desired usage level) that, in turn, is fed from the accumulator, where the
compressed air is stored. If the user draws a large enough quantity of
compressed air from the system (from the accumulator), a sensing device
within the accumulator will send a signal to the air compressor to start,
which will produce compressed air to recharge the accumulator. In addi-
tion to providing service in airlines, pressure-regulating valves are also
used in liquid lines. The operating principle is much the same for both
types of service. Simply, the valve is set to monitor the line and to make
needed adjustments in response to a signal from a sensing device.
Temperature-regulating
valves (also referred to as
thermostatic
control valves
) are closely related to pressure-regulating valves (see
Figure 4.36). Their purpose is to monitor the temperature in a line or
process solution tank and to regulate it—to raise or lower the temper-
ature as required. In wastewater operations, probably the most famil-
iar application for temperature-regulating valves (see Figure 4.37) is
in
heat exchangers
. A heat exchanger type of water system utilizes a
water-to-coolant heat exchanger for heat dissipation. This is an efficient
and effective method to dispose of unwanted heat. Heat exchangers are
equipped with temperature-regulating valves that automatically modu-
late the shop process water, limiting usage to just what is required to
achieve the desired coolant temperature.
4.13.2.11 Relief Valves
Some fluid power systems, even when operating normally, may tem-
porarily develop excessive pressure; for example, whenever an unusu-
ally strong work resistance is encountered, dangerously high pressure
