Ingeniera

Pressure & Flame Protection

Tank Protection Valves

Ta n k P r o t e c t i o n V a l v e s

Pressure/Vacuum Relief Valves - A range of pressure only,
vacuum only and combined pressure and vacuum relief valves to
alleviate the problems caused by the thermal effects and the
filling and emptying of storage tanks and vessels.
Combination Flame Arresters/Relief Valves A comprehensive rangeof Flame Arresters is available to work in
combination with the MARVAC Pressure/Vacuum Relief Valves
(see picture).

Pilot Operated Relief Valves - To provide accurate pressure
relief when operating near to the design pressure of the tank and
also to overcome the problems of backpressure generated at the
discharge of the valve due to pipework, scrubbers etc.

Tank Blanketing Valves -Dedicated to provide inert or rich
blanketing of storage tanks to reduce harmful fugitive emissions
and reduce the evaporation of product.

Emergency Vent Manway and Gauge Hatch - To provide
over pressure protection in the event of the tank being subjected
to fire exposure and to provide access to the vessel from the
top for internal inspection.
Gauge hatches to provide for product levelmeasurement and
sampling.

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CONTENTS
Page

Ta n k P r o t e c t i o n V a l v e s

3-6
7-10
11-18
18-19
20

Introduction
How they work
Dimensions and weights
Accessories
Materials

24
25
26
27
28
29

Sizing
Determination of venting requirement
- API 2000
Wetted surface area calculation
Gas flow conversion
Tank blanketing valve sizing
API 2000 Formula
CoefficientsUseful vapour and gas data

30-33

Capacity
Air capacity tables

34
35

Terms, Definitions and Conversions
Useful terms and definitions
Useful conversions

36
36

Transportation Protection
‘Megaflo’ P/V Valve
‘Tank-A-Vent’ Bursting Disc

37

Combination Valves
Combination Flame Arresters/Relief Valves

21-23

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INTRODUCTION
Marvac manufacture an extensive range ofproducts to
protect low pressure storage tanks and vessels. These
products help to prevent damage to the tank and also
prevent the tanks contents from escaping, ensuring the
safety of personnel and the surrounding environment.

Marvac design and manufacture valves to
ISO9001:2008 in different configurations to suit a
variety of applications.These valves are compliant
with the EuropeanATEX and PED directives when
applicable.The Marvac range is also GOST-R
approved.
Pressure/Vacuum valves are designed to limit the
maximum pressure and vacuum that can exist in a tank.
When a tank is being filled the gas (air, vapour, etc.)
that filled the space above the liquid is compressed and
if this pressure was allowed to exceed the design
pressure of the tank, then it would explode.Also, if
the temperature of the tank increases, then the effect
of vaporisation and expansion would cause the pressure
to rise. Conversely, emptying the tank, or a reduction
in temperature, causes a vacuum to be created.
If the stored liquid is not volatile then the tank can be
allowed to breathe through a free vent (fig 750). This is
effectively an orifice with a hood and screen to keepout rain and birds. However, if the liquid is volatile then a
free vent will allow valuable product vapour to be emitted
to the atmosphere.
Fitting a relief valve allows the pressure in the tank to be
increased above atmospheric. Such an increase in
pressure, increases the boiling point of the liquid, reducing
the amount of vapour which would otherwise form.
When the relief valve does liftit will predominantly
discharge air rather than product vapour.
Pressure/Vacuum Relief Valves
The Marvac range of pressure only, vacuum only and
combined pressure and vacuum relief valves, can be
weight, spring or pilot operated. A Pressure/Vacuum

valve is designed to breathe out during tank filling and
breathe in while the tank is being emptied.

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