What is a Pressure Tap?
A pressure tap, or static pressure trap, is an opening within the barrier or wall that binds the flow of a material. This material being stopped by the tap may be a gas or liquid that is used to gauge and measure the amount of pressure pushing the material through the system. The opening made by the tap is always perpendicular to the direction of the flow within the system to prevent interruption of the flow. Pressure tap systems are also commonly referred to as piezometer openings, as piezometer units may be installed at the openings to measure the amount of static pressure within the system.
Pressure taps are commonly used in systems with flows that are pressurized to the point that they create noise within the system that translates to noise outside of the system. For instance, some vehicles require these taps in the exhaust system before the muffler unit to reduce the amount of pressure pushed into the muffler through the exhaust tubing. In this case, the pressure tap is used to gauge as well as release excess pressure from the system so both noise and the probability of damage to the exhaust system or engine are decreased substantially.
One of the most important considerations when working with pressure taps is that the direction of the tap must be perfectly perpendicular with the flow of the material as well as with the material the wall of the system is manufactured out of. Any directional variance in the tap within the system will create either drag or flow, allowing air to enter the system in a directional manner. This could change or disrupt the amount of pressure as well as the flow of the material.
The hole that is used to create the pressure tap being perpendicular to the flow creates a means of allowing the material to pass through the system without any variance or interruption to the flow of the system material. The diameter of the hole determines at what point the hole becomes a means of escape of excess material or at what point pressure is relieved once the allowed amount of pressure is exceeded within the system. In order to ensure the proper installation of a pressure tap, a pressure tap machine or jig that ensures the perfect perpendicularity of the tap into the system is created upon the drilling or tapping of the system.
@miriam98 - I think it should be pointed out that whatever you are using a pressure tap for, you need to be careful about determining the correct size of the hole.
If you make the hole too big, you might allow foreign debris to enter into the system. Too much of this debris will clog it up and violate one of the premises behind the pressure tap; that it should not interrupt the flow of the current, whether it’s water or gas or whatever.
@NathanG - That would make sense. In any situation where you're using piezometers as pressure taps, I do believe that the location of the pressure tap on the unit might affect the effectiveness of the gauge.
For example, do you locate the pressure tap further upstream in the current or further downstream in the current?
Take an oxygen sensor on the catalytic converter for example. Its purpose is to measure the oxygen going through the converter. I think they place the sensor at specific locations along the catalytic converter, to ensure that they get the most accurate readings.
I wouldn’t place it near the front of the catalytic converter. Exhausts are just entering the system. I think near the middle or slightly past the middle would give you the most accurate readings.
I’ve heard that if you have a really "souped up" sports car, then installing a pressure tap in the muffler can help relieve fuel pressure. I’ve never done it, but it makes sense.
However, if you decide to do that, make sure you pick the area of the muffler where the pressure tap will occupy the most space. That will give you maximum effect.
In addition to relieving the pressure, it should result in less noise from the muffler, which is a nice side benefit in my opinion.
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