00:00This is a Boudon tube type pressure gauge. It is a mechanical pressure measuring instrument that
00:06operates without electricity. In this video we'll take a close look at the mechanism inside to see
00:12how it works. Before we jump into the inner workings of a pressure gauge, let's first see
00:16what are the key external components involved. Let's get started. This is the socket. It features
00:23a small hole at the base, allowing the fluid whose pressure we want to measure to enter the
00:29pressure sensing element inside the gauge. The socket's external threads serve the purpose of
00:35mounting the gauge onto the process connection port. This enables precise pressure measurements
00:41at specific points within the system. A pressure gauge is a device that measures the pressure of
00:47a fluid in a system. The fluid can be a gas or a liquid. Fluid pressure refers to the measurement
00:53of the force per unit area exerted by the fluid on a given object.
00:59This is the pointer and the dial. The pointer is connected to the internal mechanism and moves
01:04across a calibrated scale on the dial in response to the variation of pressure. Users can read
01:10the pressure value directly from the dial, where the pointer indicates the pressure currently
01:15prevailing. On the dial we also find other information like the unit in which the pressure is measured.
01:21A pressure gauge can be dry or filled with liquid on the inside. Wet gauges have a fill plug that
01:28is also used for venting the gauge. Temperature variations during shipment and operation can cause
01:34the liquid fill to expand and contract, changing the pressure inside the sealed case, which can reduce
01:40the accuracy of the reading. Venting is sometimes required to release excess pressure. We will look at
01:47the reasons we use dry versus liquid filled gauges in more detail later in this video.
01:52Some pressure gauges have a blowout plug on the back. They act as a pressure relief mechanism designed
01:58to release the overpressure away from the operator in the event of a catastrophic failure of the pressure
02:04sensing element inside the gauge. Now let's look at the mechanism inside the pressure gauge. This is the
02:11pressure sensing element called a Boudon tube. It's a C-shaped thin walled metallic tube with an oval
02:17cross section. Its working principle is based on the elastic deformation of a curved, flattened tube
02:23when subjected to pressure. The tube deformation is proportional to the applied pressure. The fixed
02:30end of the Boudon tube is mounted to the socket base and the moving sealed end is connected to a mechanism
02:36that translates the small deformation of the tube into a rotary movement for the pointer. As the Boudon tube
02:44straightens, it transmits its linear motion through the connecting link. That drives the sector gear. That
02:50meshes with the pinion driving the pointer. When the pressure decreases, the Boudon tube returns to its
02:56original shape and the pointer goes back to its zero position on the dial with the help of the spiral torsion
03:03spring. There are various types of pressure gauges which use different principles for sensing pressure.
03:08The C-shaped Boudon tube type is the most common one. Before we take a look at dry versus oil-filled
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04:27mechanics of pressure gauges. Dry pressure gauges are best suited for dry environments but are sensitive
04:34to high physical stress. One of the main advantages of wet gauges is that the liquid dampens vibrations and
04:40pressure spikes, preventing them from being transferred to the internal mechanism. Additionally, it stabilizes the
04:47pointer, enhancing the readability of the pressure on the dial. Liquid-filled gauges are typically filled
04:53with glycerine, or silicon oil, which lubricates the internal components, reduces wear, and increases
04:59the lifespan of the gauge. They are not filled to the brim to prevent leaks when the liquid expands. Lastly,
05:06wet gauges prevent condensation from forming inside the gauge. I hope you found this video informative and
05:12interesting. If you did, don't forget to give it a thumbs up and subscribe.
