Proper Start-up – Basic Gas pressure

Let’s start with gas pressure.

You probably are saying  why? Doesn’t the valve manufacturer and unit manufacturer set those up? That answer is yes & no!  The valves are “factory set” based on a set of parameters in their particular design.  That is usually set based in the inlet pressure to the valve to provide a certain outlet or manifold pressure at that inlet pressure. Both the gas valve manufacturer and equipment manufacturer do not know the specific pressure at the installation site – both commercially and residentially.

A lot of commercial buildings have “high pressure gas” services to the building.  This is great because it allows smaller gas piping to be run to the equipment and keeps the installation cost down BUT, there then needs to be a pressure regulator at each piece of equipment. Based on the incoming building pressure, the regulator has to be of proper size and then adjusted to the proper outlet pressure (see post on gas pressure regulators). This outlet pressure from the regulator, now becomes the inlet pressure for the unit.  Most manufacturers allow a range of 6 IWC minimum to a maximum of 11 IWC for inlet pressure.  If the inlet pressure exceeds the 11 IWC — the valve may not open or it could cause unsafe ignition or ignition lock-outs, limit trips, etc..

On a unit with a pilot, the pilot is usually unregulated  (adjusted with a simple needle valve in the main gas valve) and now the pilot valve opens, and the unit has a ‘torch” for a pilot flame.  This, in turn, trips the roll-out switch and the unit is locked out. Or the pilot lifts off the pilot burner or cross-over and the micro-amp signal to ground is lost because the flame no longer makes contact with the unit and ground.

If the building does not have high pressure gas, the inlet pressure still needs to be checked with all the building equipment running to make sure it does not drop below the minimum required for safe lighting if everything in the building were to be on at the same time.

Then the main valve needs to be checked and set to the manufacturer’s specifications for proper outlet or manifold pressure. Depending, today, on how many stages of heat are available (or if it is modulating heat like a lot of new equipment is starting to use on both commercial and residential units) the HIGH FIRE manifold pressure needs to be set. On some multi-stage units, the low fire also needs to be set — some are “self-adjusting”  when the high fire is set so you need to see what your manufacturer recommends. In all cases, whether residential or commercial, the high fire will always need to be properly adjusted.

So, hopefully you now see that if you  still think the unit can just be set and you never check the gas pressure that you could be over-fired, under-fired, have roll-out switch issues, have flame rectification issues, unsafe lighting characteristics of the burners, and on and on and on!

In the next post on Proper Start-ups — Basics, we’ll explore some more reasons why the equipment is not just “plug and play” or “set & run” “and see what else is part of a PROPER START-UP!


About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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One Response to Proper Start-up – Basic Gas pressure

  1. Joe says:

    Another great post, one should never assume, and proper start up time and troubleshooting should be accounted for. Thanks again Mr. Martin

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