Groth 1201B - Manual (Page 4)

4
DESIGN, FUNCTION & OPERATION
Pressure Relief: As the pressure in the storage tank
increases the vacuum pallet is held shut. When the
set pressure is reached the pressure pallet lifts and
relieves to a header (or to atmosphere if it is not a pipe
away valve).
Vacuum Relief: As a vacuum is drawn on the
storage tank (for example, when fluid is being
pumped out), the pressure pallet is held shut by
tank vacuum. When the vacuum setting is
reached, the pallet lifts and air is drawn in from
the atmosphere and flows into the tank.
NOTE 1: Minimum recommended clearance between vacuum inlet port and tank roof is nominal flange bore of valve.
Typical valve installation on a tank or vessel is illustrated in Fig.1 on the next page using a Model 1221A
Pressure/Vacuum Relief Valve. Most tanks will have provision for an operating relief valve, an emergency relief
valve, and a blanketing regulator that maintains a positive gas pressure in the tank.
The combination of these valves and regulator are designed to ensure that the tank is protected from both excess
vacuum and pressure conditions.
Figure 1 - Typical Tank Installation
Tank protection equipment typically includes an operating valve which is designed to provide pressure/vacuum relief
under normal pump in/out and thermal breathing conditions. An emergency relief valve can also provide both
pressure and vacuum relief, normally sized to provide pressure relief if there is a fire in the immediate vicinity of the
tank. It may also be sized by the tank designer to provide protection in the event of equipment failure (such as the
rupture of a process steam line or an inert gas blanketing system failing “wide open”) or operator error.
A typical tank installation is shown in Fig. 1 which includes the following Groth products:

Model 1221B PV’ Valve

Model 3011 Blanket Gas Regulator

Model 2400 Emergency Relief Valve