NZQA registered unit standard
Title
2638 version 6
Page 1 of 4
Demonstrate knowledge of control valves, actuators, and positioners
Level
Purpose
3 Credits 4
People credited with this unit standard are able to demonstrate knowledge of:

control valves;

control valve sizing for liquid flow;

valve actuators; and

valve positioners.
Classification
Industrial Measurement and Control > Industrial Measurement and Control - Theory
Available grade Achieved
Explanatory note
1 Reference
ANSI/ISA-75.05.01-2000 (R2005) Control Valve Terminology ; and all subsequent amendments and replacements.
Outcome 1
Demonstrate knowledge of control valves.
Evidence requirements
1.1 Define terms associated with control valve components.
Range trim (wetted parts), stem packing, yoke, plug, seat.
1.2 Describe control valve types and compare their features.
Range linear – single seated globe, double seated, saunders, cage guided, multi-orifice; rotary
– ball, butterfly, eccentric rotary plug.
1.3 Describe control valve inherent flow versus lift pressure drop conditions. characteristics under constant
Range linear, equal percentage, quick opening.
The Skills Organisation
SSB Code 100401

New Zealand Qualifications Authority 2020

3.3
3.4
NZQA registered unit standard 2638 version 6
Page 2 of 4
1.4
1.5
Describe control valve installed flow versus lift characteristics.
Explain t he terms ‘rangeability’ and ‘turndown’ in the context of control valve operation.
1.6 Describe damage associated with control valves and describe causes.
Range
Outcome 2 erosion, corrosion, cavitation, flashing, wear.
Demonstrate knowledge of control valve sizing for liquid flow.
Evidence requirements
2.1 Calculate control valve sizes for liquid flow, based on valve sizing coefficients
C v
(imperial), A v
(metric), or K v
(metric).
2.2 Calculate size of control valve, based on differential pressure and flow with the valve fully open.
Range differential pressure (pounds per square inch - psi); flow (US gallons per minute); C v
, A v
, or K v
.
Outcome 3
Demonstrate knowledge of valve actuators.
Evidence requirements
3.1 Explain air operated control valve actuators.
Range diaphragm, single acting piston spring return, double acting, pressures, bench set.
3.2 Describe electrically operated control valve actuators.
Range motorised valves, solenoid valves.
Describe hydraulic and electro-hydraulic actuators and servo valves.
Compare features of control valve actuator types.
Range diaphragm, piston, operating pressures, size, electric, hydraulic.
The Skills Organisation
SSB Code 100401

New Zealand Qualifications Authority 2020

NZQA registered unit standard 2638 version 6
Page 3 of 4
Outcome 4
Demonstrate knowledge of valve positioners.
Evidence requirements
4.1 Explain reasons for using control valve positioners.
Range stem friction, long transmission lines, split range control valves, characterising stem movement, change pressure range, double acting piston actuator.
4.2 Describe control valve positioners.
Range electro-pneumatic (4-20mA input), digital valve controllers, motion balance, force balance, double acting (5 port spool valve).
Planned review date 31 December 2017
Status information and last date for assessment for superseded versions
Process Version Date Last Date for Assessment
Registration
Revision
1
2
31 October 1995
30 October 1997
31 December 2013
31 December 2013
Revision
Review
3
4
3 April 2001
22 June 2001
31 December 2013
31 December 2013
Review 5 19 May 2008 31 December 2019
Review 6 28 November 2013 N/A
Consent and Moderation Requirements (CMR) reference 0003
This CMR can be accessed at http://www.nzqa.govt.nz/framework/search/index.do
.
Please note
Providers must be granted consent to assess against standards (accredited) by NZQA, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be granted consent to assess against standards by
NZQA before they can register credits from assessment against unit standards.
Providers and Industry Training Organisations, which have been granted consent and which are assessing against unit standards must engage with the moderation system that applies to those standards.
Requirements for consent to assess and an outline of the moderation system that applies to this standard are outlined in the Consent and Moderation Requirements (CMR). The
CMR also includes useful information about special requirements for organisations wishing
The Skills Organisation
SSB Code 100401

New Zealand Qualifications Authority 2020

NZQA registered unit standard 2638 version 6
Page 4 of 4 to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements.
Comments on this unit standard
Please contact The Skills Organisation reviewcomments@skills.org.nz
if you wish to suggest changes to the content of this unit standard.
The Skills Organisation
SSB Code 100401

New Zealand Qualifications Authority 2020