17-01_Terminology.pdf

Terminology | LESER GmbH & Co. KG | 20.06.2013 | Rev. 01
Terminology

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
2 / 29
Objectives of this Presentation
Knowledge to learn
The aim of this presentation is to explain
the most common phrases around Safety Valves.
Objectives

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
3 / 29
Organizations and
Associations
ISO 4126 International Organization for
Standardization
Manufacturer
American Petroleum Institute
(API)
API 520, 526, 527
International
National Engineering
Research Center for
Special Pump & Valve
(NERCSPV)
General Administration of
Quality Supervision,
Inspection and Quarantine/
Special Equipment Licensing
Office (AQSIQ SELO)
GB/T 12242 and Safety
Valves General
Requirements GB/T
12241
China
Office appointed
(e.g. German Technical
Inspection Association)
European Council/ European
Parliament
Pressure Device Guideline
– 97/23/EG, new from
19.07.2016: 2014/68/EU
Europe
National Board (NB)
American Society of
Mechanical Engineers
(ASME)
ASME Section VIII
Division 1
USA
Monitoring
organisation
Symbol
Issuer of regulations
Applicable regulations
Area of
application
Institutions, Standards and Regulations

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
4 / 29
Classification of safety devices
Classification of
Safety Devices
Pressure Relief Devices
Reclosing Devices Non-reclosing Devices
Direct-load Controlled
Controlled Safety Pressure Relief System
Spring
loaded
Weight
loaded
Relief
Valve*
Safety
Valve*
Safety
Relief
Valve*
Pilot-Operated Safety Valve
Snap-acting Modulating
Rupture Disc
Function
Loading
Principle
Pin-actuated Device
*acc. to ASME

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
5 / 29
Definition of Terms
Pressure Relief Devices
A pressure relief device designed to open and relieve excess pressure
and to re-close and prevent the further flow of fluid after normal
conditions have been restored.
Definition of Terms

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
6 / 29
Loading Principle
Spring Loaded Pressure Relief Valves
A pressure relief valve in which the opening and closing
of the valve is controlled by a spring.
Loading Principle

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
7 / 29
Loading Principle
Weight Loaded Pressure Relief Valve
Loading Principle
A pressure relief valve in which the opening and closing
of the valve is controlled by a weight.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
8 / 29
Loading Principle
Pilot-Operated Safety Valves
Loading Principle
A pressure relief valve in which the main valve is combined with and
controlled by an auxiliary pressure relief valve (pilot-controlled).

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
9 / 29
Loading Principle
Controlled Safety Valve System
Loading Principle
A system consisting of a safety valve in combination with control unit.
The control unit generates an additional closing force with the aid of a
drive in the case of a spring-loaded safety valve.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
10 / 29
Loading Principle
Rupture Disc / Safety Valve Combination
Loading Principle
A system consisting of a main valve in combination with a
prepended rupture disc. The bursting pressure of the rupture disc is
equal to the set pressure of the safety valve.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
11 / 29
Opening Characteristics
Normal Safety Valve Pursuant to AD 2000 Information Sheet A2
Opening
Characteristics
A spring loaded pressure relief valve actuated by the static pressure
upstream of the valve. The valve opens in proportion to the pressure
increase over the opening pressure. Used primarily with liquid service
(non-compressible).
p = set pressure pc = opening pressure
pp = popping pressure ps = closing pressure
90 100 110
Lift [%]
Pressure [%]
100
80
60
40
20
0
p
p
p
c
s

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
12 / 29
Standard 10% – Pop-Acting
80 90 100 105 110 120
Lift [%]
Pressure [%]
100
80
60
40
20
0
p
p
p
p
c
s
p
Normal Safety Valve Pursuant to AD 2000 Information Sheet A2
A spring-loaded normal safety valve opening proportionately or suddenly
within a pressure increase of 10%.
Used with all media: steam, vapour, gas and liquids.
Opening
Characteristics

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
13 / 29
Sudden opening within 5%
80 90 100 105 110 120
Lift [%]
Pressure [%]
100
80
60
40
20
0
p
p
p
p
c
s
p
Full-lift Safety Valve Pursuant to AD 2000 Information Sheet A2
A spring-loaded full-lift safety valve opening suddenly within a pressure
increase of 5%.
Primarily used for gas, steam and vapour.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
14 / 29
Definition of Terms
Conventional Pressure Relief Valve
A spring loaded pressure
relief valve whose operational
characteristics are directly
affected by changes in the
back pressure on the valve.
Definition of Terms
Cap H2
Lock nut
Adjusting screw
Needle bearing
Spring plate
Spring
Spindle
Bonnet
Split ring
Spring plate
Stud
Nut
Guide
Gasket
Bellows
Screw
Ball
Lock screw
Disc
Adjusting ring
Body
Nozzle

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
15 / 29
Cap H2
Lock nut
Adjusting screw
Needle bearing
Spring plate
Spring
Spindle
Bonnet
Split ring
Spring plate
Stud
Nut
Guide
Gasket
Lift stopper
Screw
Ball
Lock screw
Disc
Adjusting ring
Body
Nozzle
Definition of Terms
Balanced Pressure Relief Valve
Definition of Terms
A spring loaded pressure relief
valve that incorporates a
bellows or other means for
minimizing the effect of back
pressure on the operational
characteristics of the valve.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
16 / 29
Definition of Terms
Valve Seat
Definition of Terms
The area of contact between the valve nozzle and disc.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
17 / 29
Definition of Terms
Set Pressure
Definition of Terms
The inlet gauge pressure at which the Pressure Relief Valve is set to open.
 Each manufacturer defines set pressure differently
 LESER defines set pressure as:
– Initial Audible discharge for vapor/gas/steam
– First Steady Stream for liquids
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%)
Pressure (%)
Competitors LESER
Set to pop Set to initial audible discharge

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
18 / 29
Definition of Terms
Definition of Terms
Simmer
The audible or visible escape of compressible fluid between
the seat and disc of the Pressure Relief Valve prior to set-point:
 LESER valves do NOT simmer before reaching the set pressure,
unlike some of our competitors
 Competitor’s typical values are between 93 and 98%
(depending on valve design)
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%)
Pressure (%)
Competitors LESER
Simmer

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
19 / 29
Definition of Terms
Cold Differential Test Pressure (CDTP)
Definition of Terms
The pressure at which a Pressure Relief Valve is adjusted to open
on the test stand. It includes corrections for the service conditions
of constant back pressure or temperature or both.
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 112
Lift (%)
Pressure (%)
Set pressure CDTP

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
20 / 29
Definition of Terms
Opening Pressure Difference
Definition of Terms
The pressure increase over the set pressure of the safety valve
that thus allows the rated flow to be achieved.
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%)
Pressure (%)
Opening
pressure difference max. 10 %

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
21 / 29
0
20
40
60
80
100
76 78 80 82 84 86 88 90 92 94 98 100
Lift (%)
Definition of Terms
Definition of Terms
Closing Pressure Difference
The difference between the set pressure and the closing pressure
of a safety valve (expressed as a percentage of set pressure).
Vessel
pressure (%)
Closing
pressure
difference

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
22 / 29
Definition of Terms
Definition of Terms
 Maximum Allowable Working Pressure (MAWP)
The maximum gauge pressure allowed at the top of a completed vessel.
Design pressure may be used instead of MAWP in all cases where the MAWP
has not been established. Design pressure is equal to or less than MAWP.
 Accumulation
The pressure increase over the MAWP of the vessel allowed during discharge
through the Pressure Relief Valve (governed by applicable codes).
 Maximum Allowable Accumulated Pressure
The sum of the MAWP and the accumulation.
0
20
40
60
80
100
82 84 86 88 90 92 94 96 98 100 102 104 106 108 110 121
Lift (%)
Vessel
Pressure (%)
Operating Pressure
Maximum Allowable
Working Pressure
Maximum Allowable Accumulation
Pressure Single Valve

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
23 / 29
Definition of Terms
Definition of Terms
Operating Pressure Ratio
The ratio of operating pressure to set pressure.
90% should not be exceeded.
0
20
40
60
80
100
82 84 86 88 90 92 94 96 98 100 102 104 106 108 110 121
Lift (%)
Vessel
Pressure (%)
Operating
Pressure
Maximum Allowable
Working Pressure
Operating
Pressure
Ratio

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
24 / 29
Definition of Terms
Definition of Terms
 Flutter
The abnormal, rapid reciprocating motion of the movable parts
of a pressure relief valve in which the disc does NOT contact the nozzle
 Chatter
The abnormal, rapid reciprocating motion of the movable parts
of a pressure relief valve in which the disc contacts the nozzle
Possible causes for the above include:
– Inlet pressure drop too high
– Excessive back pressure
– Oversized valve
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%)
Vessel Pressure (%)
Flutter
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%)
Vessel Pressure (%)
Chatter

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
25 / 29
Definition of Terms
Definition of Terms
Actual (ASME) Discharge area
The minimum net area that determines
the flow through the valve.
D

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
26 / 29
Definition of Terms
Definition of Terms
 Effective Discharge Area
The theoretical area of flow through a pressure
relief valve, as defined in API 526:
– independent of any specific valve design
or manufacturer
– Used in API sizing calculations for orifice selection
 Effective Coefficient of Discharge
The nominal value used with an effective
discharge area to calculate the minimum
required relieving capacity of a pressure
relief valve:
– 0.975 vapor/gas/steam
– 0.65 liquids

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
27 / 29
Definition of Terms
Definition of Terms
 Coefficient of Discharge (Kd)
The actual discharge flow divided by the theoretical discharge flow
 Rated Reduced Coefficient of Discharge (Kdr)
The product of the coefficient of discharge (Kd) x 0.9.
The rated reduced coefficient of discharge is to be used for all sizing
calculations.

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
28 / 29
Definition of Terms
Definition of Terms
LESER Effective Orifice (LEO) area
 Pressure relief devices may be initially sized
using the API effective coefficient of discharge
(S/G 0.975, L 0.650) and effective areas
(acc. to API Std. 526), which are independent
of any specific valve design.
 In this way the engineer can determine
a preliminary pressure relief valve size.
By using the LESER Effective Orifice (LEO),
the engineer can conveniently select
a LESER safety relief valve after calculating
the API required orifice area.
 Where:
– LEOS/G = LESER Effective Orifice
(for steam, gas and vapor) [inch²]
– LEOL = LESER Effective Orifice (for liquid) [inch²]
– K = de-rated coefficient of discharge, taken from
Red Book Pressure Relief Device Certifications
(NB-18)
– A0 = actual orifice [in²]

Objectives
Definition of Terms
Classification of
Safety Devices
Organizations and
Associations
Loading Principle
Opening
Characteristics
Definition of Terms
Definition of
Back Pressure
29 / 29
Definition of
Back Pressure
Definition of Back Pressure
 Back Pressure
The pressure that exists at the outlet
of a Pressure Relief Valve as a result
of the pressure in the discharge system.
It is the sum of the superimposed and
built-up back pressures.
 Built-up Back Pressure
The increase in pressure at the outlet
of a Pressure Relief Valve that develops
as a result of flow after the Pressure Relief
Valve opens. Always variable!
 Superimposed Back Pressure
The static pressure that exists at the
outlet of the Pressure Relief Valve at
the time the valve is required to operate.
It is the result of pressure in the discharge
system coming from other sources and
may be constant, variable or both.
Note: The variable portion of the back pressure should not
exceed the allowable accumulation; otherwise, a bellows
or Pilot-Operated Safety Valve should be used.
Back Pressure =
Built-up +
Superimposed

17-01_Terminology.pdf

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