Measure DiffPressure

Theboss

Member

T

Join Date

Jun 2010

Location

Durban

Posts

159

• Aug 30, 2012

• #1

Hi guys, i'm not too sure of how would a purge system work when measuring diff pressure. does the purge system keep the impulse lines clean, can someone elaborate further as to its principal operation??? tnx in advance

 

Liam Moran

Lifetime Supporting Member

Join Date

May 2011

Location

Carlow

Posts

401

• Aug 30, 2012

• #2

I think you need to add some more detail.
I for one, have no idea of the system you are looking for help on.
Providing more detail regarding the process would help in your getting an answer.

 

MorphuisOGrady

Member

M

Join Date

Jul 2007

Location

Kiruna

Posts

600

• Aug 30, 2012

• #3

A purge systems principal operation is t flush electrical control equipment with clean air before it is turned on.

Have you a blower application you need specific answers for?

 

Theboss

Member

OP

T

Join Date

Jun 2010

Location

Durban

Posts

159

• Aug 30, 2012

• #4

its a dp cell measuring pressure across a selox(classifier) and the impulse lines are getting blocked, so i know of a purge system that is used to keep the lines clear of blockages, using compressed air, being purged continuously through a variable air regulator / flow meter ???

 

Last edited: Aug 30, 2012

rootboy

Lifetime Supporting Member

Join Date

Jan 2004

Location

Tennessee

Posts

1,375

• Aug 30, 2012

• #5

This help?


http://www.airmonitor.com/pdfs/powe...Q004_Continuous_Protective_Purge_Pressure.pdf

 

MorphuisOGrady

Member

M

Join Date

Jul 2007

Location

Kiruna

Posts

600

• Aug 30, 2012

• #6

Theboss said:

its a dp cell measuring pressure across a selox(classifier) and the impulse lines are getting blocked, so i know of a purge system that is used to keep the lines clear of blockages, using compressed air, being purged continuously through a variable air regulator / flow meter ???

Click to expand...

I'm sorry but I really don't understand the question you are asking.

You know of a purge system. What is your question? Do you need to know how to design such a system?

 

Theboss

Member

OP

T

Join Date

Jun 2010

Location

Durban

Posts

159

• Aug 30, 2012

• #7

no i need to know the principle of operation and how it really works? i have an idea tho...

 

MorphuisOGrady

Member

M

Join Date

Jul 2007

Location

Kiruna

Posts

600

• Aug 30, 2012

• #8

Here is a good place to start.

http://en.wikipedia.org/wiki/Air_purge_system

 

Mickey

Lifetime Supporting Member

Join Date

May 2003

Location

Palmdale,Ca

Posts

10,660

• Aug 30, 2012

• #9

Theboss said:

no i need to know the principle of operation and how it really works? i have an idea tho...

Click to expand...

rootboy's post #5 gives you the answer.

http://www.plctalk.net/qanda/showpost.php?p=500757&postcount=5

Here is another good read.

http://www.idc-online.com/technical...entation/Differential pressure meters_nel.pdf

And more...

http://www.google.com/#hl=en&sclien...pw.r_qf.&fp=68f623bcfb04de2b&biw=1589&bih=807

 

Last edited: Aug 30, 2012

danw

Lifetime Supporting Member

Join Date

Oct 2004

Location

midwest, USA

Posts

3,429

• Aug 30, 2012

• #10

If you're talking about purging the DP impulse lines to keep them from clogging, then there is a means of doing so.

The images below are generally for purging impulse lines across an orifice plate, attached to orifice flange unions, and some graphics refer to flow transmitters, but the concept is identical for measuring across a filter.

The text recommends "constant flow" regulators (also known as differential regulators), not constant pressure regulators.

 

shooter

Member

S

Join Date

Sep 2002

Location

duketown

Posts

2,711

• Aug 31, 2012

• #11

danw gives the good answer.
while measuring the airflow should be minimum or even closed.
you must use two restrictions.

 

Theboss

Member

OP

T

Join Date

Jun 2010

Location

Durban

Posts

159

• Sep 3, 2012

• #12

Hi Dan, this is exactly what I'm looking for, if possible can you forward me an electronic copy of the manual you quoted or a download link would be great, thank you, really appreciate your efforts.

 

danw

Lifetime Supporting Member

Join Date

Oct 2004

Location

midwest, USA

Posts

3,429

• Sep 3, 2012

• #13

For the most part, those are images I scanned and saved from older instrumentation books.

The first graphic is from Dwyer Instrument's model RKA differential regulator installation sheet.

The text (h) Purging and graphic (pg 71) are from the same book, a relatively rare book in the US, Installation of Instrumentation and Process Control Systems, EEUA Handbook No. 34, 1973, published for Engineering Equipment Users Association by Constable & Company, Ltd.

I can't recall where the 4th graphic, pg 223, came from.

A discussion of continuous purging vs blast purging is attached.

 

Theboss

Member

OP

T

Join Date

Jun 2010

Location

Durban

Posts

159

• Sep 3, 2012

• #14

is it still possible to use a purge system with pressures of -1 to -3kpa across a dp?

 

Lancie1

Lifetime Supporting Member

Join Date

Jul 2003

Location

Alabama

Posts

9,999

• Sep 3, 2012

• #15

is it still possible to use a purge system with pressures of -1 to -3kpa across a dp?

Click to expand...

Yes, if the purge pressure is sligltly "higher". Where the purge would interfere with a correct reading, you need a switching contactor that cuts purge solenoid off for some time period while a process pressure reading is being made.