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Author Topic: Pressure Loss in Gas Line  (Read 4757 times)
johnrae
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« on: December 05, 2009, 12:33:57 AM »

When my plumber installed my gas system (many years ago) he used 3/4" galvanised steel line between the meter and my house - the meter being some 25+ metres down the garden.

I now want to add a different boiler system and need to satisfy myself that the line size is suitable to meet the current pressure loss standards of 1mmWG.  I suspect it isn't so may need to get  a new plumber to instal a new line (mdpe and copper)

I can locate tables for copper and mdpe but I need those for galvanised steel.

Can someone advise me where to locate suitable flow/pressure loss tables for such piping operating on natural gas at a nominal pressure. of 20mmWG

Many thanks in advance.

jack
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Alan
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« Reply #1 on: December 05, 2009, 05:45:17 PM »

Give this a try

http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_829.html

24 metre allows 28 K.W.

As a general rule one 90 deg bend is equal to 6 ft of pipe

Regards

Alan
« Last Edit: December 05, 2009, 05:50:42 PM by Alan » Logged
johnrae
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« Reply #2 on: December 05, 2009, 06:12:49 PM »

Many thanks Alan.

That's pointing my concerns in the right direction.
I believe the permitted pressure loss is a maximum of 1mm for a 20mm supply pressure.
This equates to only 12.7Pascals so I presume the tables length-to-KW ration needs dividing by around 10 (table shows KW rating for pressure loss of 125Pa)

Botton line is that my 3/4" line is evidently grossly undersized for the meter's delivery line.  Just goes to show what Scottish Gas and my corgi registered plumber turned their collective blind eyes to when they installed the system all those years ago (about 30).  At the time they installed a combination of 80,000Btu boiler (23.4KW), a Baxi Bermuda fire + back boiler and a Valor open flame fire - a total of at least 35 to 40KW.  There's no way that line could possibly have met the requirements.

I can see me having to run at least a 32mm MDPE line (28mm bore) to get my system up to spec

jack
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desperate
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« Reply #3 on: December 05, 2009, 06:29:10 PM »

I believe the permitted pressure loss is a maximum of 1mm for a 20mm supply pressure.(quote)

I think you mean 1mbar drop with a 20 mbar static pressure?

Desperate
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chickensoup
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« Reply #4 on: December 05, 2009, 06:50:51 PM »

 Evening John,
                        If your req input was 40ish kwh, that would require  approx 4.2m3/hourly consumption. You were installed 3/4" @ a distance of 25m (not taken into consideration elbows) then that pipe output alone would only give you 2.90m3/h.
 
                   If your load still requires 40 kwh then 25m would req 1" pipe alone to deliver 5.60m3/h then add the results below per fitting, to total pipe length.

         0.3m= 1x 90deg bend
         0.5m= 1x elbow
         0.5m= 1x tee

    Is 25+m the distance from the meter to the incoming secondary ECV ( emergency control valve)? is there any more pipework downstream in your home to the appliances?

              chicken

                            
« Last Edit: December 05, 2009, 07:49:29 PM by chickensoup » Logged

My first recollection of tinkering was wiring a 240v radio cord to a 9v motor to my technic Lego truck, it ended with setting the kitchen on fire!............................I couldn't sit down for two days!
chickensoup
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meus bogs clausus


« Reply #5 on: December 05, 2009, 06:54:21 PM »

 Come on Des,
                        That's 1mbr permitted working pressure loss! you haven't started on the J.D yet have you? Grin Grin

 chicken
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My first recollection of tinkering was wiring a 240v radio cord to a 9v motor to my technic Lego truck, it ended with setting the kitchen on fire!............................I couldn't sit down for two days!
johnrae
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« Reply #6 on: December 05, 2009, 07:15:23 PM »

Hi Chicken and Des

Yes typo there, I meant mB

Good question on the ECV : the only one is at the infeed to the meter !!

Seems my gut feelings on line restriction are correct

Whole thing is starting to smell and it aint mercaptan

jack
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oliver90owner
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« Reply #7 on: December 06, 2009, 09:53:25 AM »

What is the pressure difference between incoming and after meter?  Surely there will only be a difference on the inside piping to contend with until there is no regulation from the meter....and at a higher pressure the 'kW' passed will be different?

Not a gas plumber, but interested in these differences.

Regards, RAB
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johnrae
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« Reply #8 on: December 06, 2009, 10:06:24 AM »

Rab
My uderstanding is that within the limits of the meter's capability (0-6M3/Hr) the outlet pressure is governed to 20mB (+- tolerance) so any pressure loss in line from meter to appliance is the user's problem. 
jack
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