Operating pressure Ideal logic, drop at test point

[cascas]

[FONT=verdana, arial, helvetica, sans-serif]Hi, [/FONT]

[FONT=verdana, arial, helvetica, sans-serif] I have tested the Operating Pressure on ideal logic which is giving a reading of 18mbar on the test point on the isolation valve.[/FONT]

[FONT=verdana, arial, helvetica, sans-serif]The manual states, that the external gas cock could further reduce the operating pressure when measured at its test point. The pressure drop is relative to the heat input to the boiler (kW) (approx 1.5mbar),[/FONT]​

I have come across boilers where there is a pressure drop between the isolation valve and the gas valve, but cannot see how the boiler could affect the measurement at the isolation valve on the idea, as the test point is part of the valve.

Is a reading of 18mbar allowable on the ideal logic? I am considering fitting a test point on the pipework to get a accurate reading.




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[GrahamM]

If you are getting 18 mbar going into the gas valve and are getting full gas rate etc. then all is good.
Think you are looking too much into this. Do the logics not state (as the Worcesters) that you can accept a much lower than normal inlet pressure as long as operation not affected?

 

[Mike Jackson]

The isolation valve on the ideal range is incredibly restrictive. I caused all sorts of arguments when I was working for eagaheat over pressure losses through the isolation valve.

I fitted a 40Kw icos with a 28mm gas run to within 100mm of the boiler. I was getting a 2.5 mbar drop between the mater and the boiler test point. At the time warmsure were getting very picky over gas pressures and my manager said that I would need to upgrade the gas pipe. My pipe sizing calcs showed that the pipe was adequately sized so instead of upgrading the pipe I fitted a test point just before the boiler. Testing at this point showed a drop of around 1/2 mbar.

This then caused all sorts of grief. Engineers had been sent back to properties and had been throwing 28mm gas in left right and centre following complaints of low working pressure from warmsure and it looked like it hadn't been necessary. Following my findings instead of re piping the gas when a complaint was received the first port of call was to fit a test point below the boiler. This resulted in over half of the low working pressure complaints being resolved without a re pipe.

After a little while of doing this all of the managers all received an e-mail from the gas compliance manager saying that the practice of fitting test points before the boiler should be stopped as it was unnecessary. One of the managers rang me to ask about the results I got from the one that I had fitted. It all went quiet from the gas compliance manager but the next then warmfront issued a directive that a test point should be fitted at the inlet to all boilers fitted to prove compliance with the 1 mbar pressure drop.

This practice continued until Ideal finally got their finger out and did some testing and supplied the pressure loss charts with their boilers.

I got quite a lot of grief from fellow engineers about having to fit the test points but it saved a lot of new gas runs and probably helped put pressure on ideal to supply the charts as, at that time, warmfont were fitting around 100,000 boilers a year, mostly Ideals.

 

[Brendan Rodgers]

Mate, 16.5mlb is perfectly fine AS PER IDEAL,, make sure you remove the crew completely not just loosen it as this as been a problem in the past. If your getting 16.5mlb at that test point, you will have 16mlb @ your valve which is tryed and tested on the bench. I nkow becouse im IDEAL TRAINED and kind of work for them. ITS ALWAYS UP TO THE MANUFACTURER, some allow as low as 12mlb, so always check but with IDEAL, i can help, The ISAR is the same, you only need 16.5mlb providing you,v got your minimum at the meter of 18mlb, if your meter presure is 20mlb, you should have 18mlb but dont worry if not, wont affect the boiler.

Brendan.

 

[cascas]

The isolation valve on the ideal range is incredibly restrictive. I caused all sorts of arguments when I was working for eagaheat over pressure losses through the isolation valve.

Any idea of the reason for the test point on the isolation valve to be so restrictive? I have seen some pressure losses on the wb, when measured at the gas valve, but would have through that the location of the ideal test point on the valve itself would not have caused a significant drop.

The pipework has been upgraded to 22mm, but as you seem to have also found the readings are lower than expected. I am considering upgrading the final 0.4m (and elbow), that is run in 15mm to 22mm.

The note in the MI is not that clear, it states that the external gas cock (assuming this refers to the isolation valve under the boiler with inbuilt test point) COULD (does it or doesnt it?) reduce the OP when measured at its test point. According to the chart, this could be just over 1.5mbar. A reading of 18mbar, could therefore be just over 19.5mbar - and ok?

 

[Backboiler]

The ISAR is the same, you only need 16.5mlb providing you,v got your minimum at the meter of 18mlb, if your meter presure is 20mlb, you should have 18mlb but dont worry if not, wont affect the boiler.

Sorry Brendan but with respect, I was taught you should have 19mbar min working pressure at the meter

 

[quality]

I have gas rated an isar (30 Kw) before checking working pressures at either end, and it was spot on but upon checking at the boiler and meter there was only 15 mb on the service / supply

 

[cascas]

I have gas rated an isar (30 Kw) before checking working pressures at either end, and it was spot on but upon checking at the boiler and meter there was only 15 mb on the service / supply

I have issues with the Ideal Independent 30 - rated at 33.7kw gross (30.4 nett)

The working pressure at the meter is 21mbar, and at the test point on the isolation valve only 18mbar. Clearly over the 1mbar drop allowed in BS6891. The MI mentions a pressure drop between the external gas cock could further reduce the operating pressure when measured at its test point however as the test point is part of the cock, I cannot see how this can be that restrictive?

I have gas rated the boiler and obtained a measurement of 2.91m3/hr. The MI show a gas rate of 3.13m3/hr (based on a lower cv of 38.7), so around 7% below MI but within a tolerance -10% / +5%

I have rechecked the pipework sizing, and calculate a 0.74mbar drop from the meter to the end of the 22mm. The final 0.4 metres is reduced to 15mm to supply the boiler with 1 elbow (effective length 0.7m) – This is outside the range of the chart which shows a max of 2.90m3/hr over 3m for 15mm – even at this rate it would cause a drop of 0.23 – total of 0.97 mbar over the system, which is within limits.

Without fitting a test point on the pipework, it not possible to confirm pressure loss over the pipework to confirm that pipe loss is less than 1mbar.

As I am achieving a gas rate within a tolerance, and 18mbar pressure at appliance (within MI specs), is the supply undersized, or are the readings some peculiarity of the ideal isolator test point? Would it be worth fitting a test point on the pipework to confirm? In this case, the final 0.4m of 15mm with elbow might as well be upgraded to 22mm at the same time - this will gain approx 0.2mbar? or should it just be noted on the benchmark?

 

[Brendan Rodgers]

The ISAR is the same, you only need 16.5mlb providing you,v got your minimum at the meter of 18mlb, if your meter presure is 20mlb, you should have 18mlb but dont worry if not, wont affect the boiler.

Sorry Brendan but with respect, I was taught you should have 19mbar min working pressure at the meter

I was toght 20mlb +/_ 2mlb @ the meter, but hey, whats a mlbar between freinds providing it dosnt effect the opperation of any other appliance...:1:
Iv just checked in my SOP FILE 16.3/16.2, STATE its currently 18mlb..

Bren.

 

[GrahamM]

I was toght 20mlb +/_ 2mlb @ the meter, but hey, whats a mlbar between freinds providing it dosnt effect the opperation of any other appliance...:1:
Iv just checked in my SOP FILE 16.3/16.2, STATE its currently 18mlb..

Bren.

Just to clear this up Bren. Do not know where you are getting an allowable WP at the meter of 18mb from, but as mentioned you are incorrect.
As per BS6400 and TB 071 acceptable WP at meter is 19-23mb which should give a range of 18-22mb at the gas inlet of the appliance.

 

[cascas]

If you are getting 18 mbar going into the gas valve and are getting full gas rate etc. then all is good.
Think you are looking too much into this. Do the logics not state (as the Worcesters) that you can accept a much lower than normal inlet pressure as long as operation not affected?

According to ideal It is the responsibility of the Gas Installer to size the gas Installer to size the gas installation pipework in accordance with BS6891:2005. Whilst the principle of the 1:1 gas valve ensures the Independent range is able to deliver it’s full output at inlet pressures as low as 14mb. Allowing for the acceptable pressure loss of 1mb across the installation pipework, it can be assumed that a minimum permitted operating pressure of 18mb will be delivered to the inlet of the appliance. (Reference BS 6400-1 Clause 6.2 Pressure Absorption)

 

[GrahamM]

There you go then. If you are getting more or less the max. gas rate and FGA readings are good, then all is well.

 

[cascas]

Even though the MI accept a lower working OP, technically this does not comply with BS6891 which only allows a 1mbar drop on pipework.

Although MI (same applies to Worcester) appear to allow a lower inlet pressure, in fact the reading is distorted by the test point causing a reading approx 1.5mbar lower than the true value. It seems strange that manufacturers do not provide a test point that provides a true reading - esp on the idea where the test point of on the external isolation valve rather than the gas valve. It seems that the only way to get a true reading is to fit a external test point on the pipework before the appliance.

Gas Safe Technical Bulletin 129 and 115

 

[cascas]

There you go then. If you are getting more or less the max. gas rate and FGA readings are good, then all is well.

Graham, what tolerance would you use for the gas rate. MI dont usually specify, and are based on a cv of 38.7 - whereas actual is around 39.2 (multiplied by a correction factor of 1.02264) - so about 3.5% difference.

 

[Mike Jackson]

Gas rates are usually +/- 5 %

 

[gasmarc]

Yes thats what I thought also not that I ever had an issue , I wonder why on combis you cant just run the hot tap and measure the temperature and flow rate job done,
can of worms coming lol

 

[Brendan Rodgers]

Just to clear this up Bren. Do not know where you are getting an allowable WP at the meter of 18mb from, but as mentioned you are incorrect.
As per BS6400 and TB 071 acceptable WP at meter is 19-23mb which should give a range of 18-22mb at the gas inlet of the appliance.

Yes your right, im getting my figures arse about face, 23-19mlb at meter thus 16.5mlb acceptable @ the boiler(IDEAL ISAR HE 24,30 and 35)

For the guy with the logic problem you can have as low as 15.9mlb @ the gasvalve for a LOGIC 35 , 16.2mlb LOGIC 30 and 16.7mlb for the LOGIC 24, Thats from tec team at IDEAL BOILERS.
The reading only has to be read at THE POINT OF CONNECTION and not at the valve this is wye some guys were fitting secondry test points so they fell within the Regs. As up to 2.1mlb can be lost from there to the valve.
Sorry for the confusion, ill make sure i wake up before i start typing next time.

Bren.:sleep1: