Calculating purge times for type X, Y and Z systems

10/21/2005


In order to calculate the amount of time it takes to complete a full purge cycle, you need to know:

%%POINT%%Enclosure volume

%%POINT%%Flow rate

%%POINT%%Purge media

Compressed instrument air

If you are using compressed instrument air to purge your enclosure, you can refer to predetermined purge times. These times are represented as a ratio of 1 minute per “X” cubic feet of enclosure volume. The “X” is a variable that changes with different size systems. This ratio is based on the NEC/NFPA-496 standards that require four volume exchanges. For IEC and EN standards, five volume exchanges must be performed. If there is a motor inside the protected enclosure, 10 volume exchanges must be performed to satisfy both NEC and IEC standards.

Inert gas and other purge media

If your purge media is something other than compressed instrument air, such as an inert gas, a density correction factor must be used to determine proper purge time. The density correction factor is determined by the expression:

Density Correction Factor = (molecular weight of air / molecular weight of protective gas)

The molecular weight of air at sea level is 29 AMUs (Atomic Mass Units). If you divide this number by the molecular weight of the protective gas used, you get a constant that is called the Density Correction Factor. Then multiply the exchange time you determined as if you were using instrument air by the correction factor.

For example, if you were using a system that required 1 minute per cubic foot of exchange time using instrument air, and your enclosure is 10 cubic feet, your standard exchange time would be 10 minutes. If you were using Nitrogen as your purge media, the correction factor would be:

(29 AMU / 28 AMU) = 1.04

The new exchange time would be:

10 minutes * 1.04 = 10.4 minute

www.am.pepperl-fuchs.com





No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
Prescriptive maintenance; Hannover Messe 2017 recap; Reduce welding errors
Safety standards and electrical test instruments; Product of the Year winners; Easy and safe electrical design
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Diagnostic functions for system safety; Specifying industrial enclosures; Effective decision support for a crisis
Transformers; Electrical system design; Selecting and sizing transformers; Grounded and ungrounded system design, Paralleling generator systems
Natural gas for tomorrow's fleets; Colleges and universities moving to CHP; Power and steam and frozen foods

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me