Gauge Manifolds: Let’s Play Games [The Art of Deception]
This is an active thread on the PROTech Boards and is an excerpt from our upcoming publication, Manifold Gauges: Φ The Definitive Guide© .
You don’t hear or read a whole lot on the actual manifold as a component I mean comparative to the amount of discussions, threads and articles about the gauge.
This is a piece out of the Manifold Gauge: The Definitive Guide that I’ve been “working” on for the past several months. In the Definitive Guide we look at the hoses, the valves, the analog, the digital and yep, you guessed it the manifold. This is practice in the art of deception at it’s best.
We’re going to play a little game here for the next few days. Take a look at the manifold below – after you get tired of looking at it – in a reply to the thread, tell me what you see wrong with it. I’ll answer it in a few days and we’ll see who’s been paying attention. 
For you old codgers, if you can’t see the manifold well enough above, click the image below to open a high resolution copy. Ready – Set………………………………….Play.
I should note this is not a machining error we are looking for. This is a deceptive design practice that we will discuss in greater detail in the Definitive Guide.
May 29, 2008 at 11:56 am
Thanks bro. I’ll have some of the more common brands that practice this method of deception cross cut to illustrate the point even further in the Guide, may post some here as well.
May 29, 2008 at 2:35 am
Sweet, I just found the thread on HVAC Pro Tech as well. Good stuff Tony!
May 28, 2008 at 1:24 pm
Yea trip a couple guys were correct. The deception is the implication that with a 3/8″ hose port comes a 3/8″ flow path bore. As the image illustrates that’s not always true.
As you know the benefit of larger bored flow paths is in the time savings in recovery and evacuation. The charging procedure effect is negligible. For a long time when the 3/8″ port on the manifold began to appear and began to get really popular, I just didn’t get it. I was following every recommended procedure and technique to effectively establish vacuum targets and/or speed the recovery procedure, provided all of these techniques were applied the 3/8″ ported manifold was supposed to enhance that speed. Wrong!!!
So I became interested in why I wasn’t seeing the benefits (reflected in time) of the 3/8″ manifold. That’s when I found out, I didn’t have a 3/8″ manifold but rather a 3/8″ ported manifold. Huge difference in the two. Look back through some of the older threads I’ve made posts about this before. This fact and the issues with valve obstruction to flow in some manifold designs is what inspired the Definitive Guide that I am working on.
The primary issue with a true 3/8″ bore manifold is it’s size. The pistons have to be bigger which makes the manifold bigger. We as technician’s want smaller and lighter. Everyone knows the PITA to haul a tool bag and a set of gauges up a ladder – so we want smaller lighter instruments and tools that will do the same thing as their larger counterparts. The instrument OEM’s, faced with sky rocketing and ever increasing raw material costs (you priced scrap brass lately)?
A true 3/8″ bore is actually .312″ – the I.D. of a standard 3/8″ SAE flare fitting, while a 1/4″ bore is 0.19″ (+/- 0.010) the standard 1/4″ I.D. of an SAE flare fitting. So expressing the values in those terms it’s easy to see why you see no difference in flow going from a .312″ inlet at the port and necking down to a 0.19″ flow path.
Yellow Jacket has a larger manifold to facilitate the 3/8″ bore and of course as I’ve always said so does J/B. So the next time you buy a manifold ask questions. Just because you see a 3/8″ port on the outside does not mean you are buying a 3/8″ manifold.
May 27, 2008 at 2:02 pm
Very good observations Rat. I will post the answer and the reasons that I refer to it as deceptive in a day or so.
May 27, 2008 at 4:05 am
Okay, I’ll play! First I see the machining hickey you mentioned, no port into the High Side gauge seat. The only other thing I can see is, possibly, that the vacuum port (3/8″ supposedly) is necked down to 1/4″ inside the manifold.