I have made a basic overview of different models and types of pressure switches. Setting the Cut-out Pressure Setting the cut-out pressure is basically the same as setting the cut-in pressure. When deciding what the best pressure is for you and your compressor, always remember to set the pressure as low as possible for your application. Thinking about it, this makes sense, as this is the most important thing for your machine to operate properly (they will operate properly on a higher pressure, but not on a lower pressure). An RT pressure switch contains a pressure operated single-pole changeover contact, the position of which depends on the pressure in the inlet connection and the set scale value. Well, from personal experience I can say that it can sometimes be quite frustrating.. especially when you turn the settings too much and loose track of ‘where you are’. Kind Code: A1 . The pressure where the compressor starts-up. Depending on how far the actual pressure is below your desired cut-in pressure, turn the screw a little further (quarter-turn or less). Difference between them, Electrical & Instrumentation QC Interview Questions, Start Stop of one Motor from the same Push button PLC program, Remote Seal Transmitters Ranging Calculation. The mercury tilt switch bottles have yellow-colored plastic caps covering up their external electrical contacts: The next set of photographs show a mercury tilt switch removed from the pressure switch mechanism, so you may see the switch in two different states (contact open on the left, and closed on the right): Advantages of mercury tilt switches include immunity to switch contact degradation from harmful atmospheres (oil mist, dirt, dust, corrosion) as well as safety in explosive atmospheres (since a spark contained within a hermetically sealed glass bulb cannot touch off an explosion in the surrounding atmosphere). Tension on the spring may be adjusted by a technician, which means the trip point of this switch is adjustable. They are mainly used for sensing a difference in pressure between two points in a plant or system. A differential pressure switch is a device which utilizes a differential air pressure to actuate an electric switch at a pre-set actuation point. For example, a high-pressure switch with a trip point of 67 PSI (changes state at 67 PSI, increasing) that re-sets back to its normal state at a pressure of 63 PSI decreasing has a “deadband” or “differential” pressure setting of 4 PSI (67 PSI − 63 PSI = 4 PSI). Close the drain valve. Turn clockwise to increase the cut-in pressure. Every increase in pressure will require more energy. Factory Setting ② The differential pick-up point is pre-set at the factory. On most (but not all…) pressure switches, the big set-screw is to set the cut-in pressure. Recall from Basics of Switches article, that the “normal” status of a switch is the resting condition of no stimulation. Basic parts of a pressure switch and how the device works. Abstract: A pressure switch includes a piston that is movably disposed in a sensor housing. This is the cut-in pressure. Ashcroft ® pressure switches are provided in a variety of configurations to meet most installation requirements in nearly every industry. The smaller screw, the differential setting, then sets the maximum pressure, the cut-out pressure, relative to the cut-in pressure. Accept Read More, Understanding High Integrity Pressure Protection Systems (HIPPS), What is FAT and SAT? Example of set-screws for cut-in and differential pressure. A great many pressure switches of this design were sold under the brand name of “Mercoid,” with a few appearing in this photograph of a steam boiler (the round-shaped units with glass covers allowing inspection of the bourdon tube and mercury tilt switch): A close-up photograph of one of these pressure switches appears here. This is better for machines that only run for a very short time. Delta P (ΔP), pressure difference or differential pressure usually refers in the technical world to the drop of pressure in a piping system, a heat exchanger or another machine, where a liquid is passing through. You have now successfully set the pressure switch. Start the compressor and let it run until it reaches the cut-out pressure. Just set the cut-in and cut-out pressures, right. This is a pre-compressed spring and the force generated by this determines the pressure at which the switch operates. Open the drain valve and wait until the pressure drops low enough to start the compressor. Some types allow adjustment of the differential. A … The procedure is somewhat the same as for the cut-in pressure. Differential pressure switch, MBC 5180 061B128066 Product name: Differential pressure switch, Type: MBC 5180, Reset function: Auto, Contact function: SPDT, Pressure connection size: 1/4, Pressure connection type: G, Pressure connection notes: With flange Open a drain to slowly let some air escape. Click the link here to view an instruction sheet that explains how to adjust a differential, vacuum, or pressure switch. A 20 psi differential is standard and recommended. Operating pressure: 360 mbar. I always tend to think think that the pressure switch sets the upper pressure limit with the main adjust screw. Adjust when necessary. Like the Danfoss gauge pressure switch seen previously, this differential pressure switch has a “trip” or “limit” setting as well as a “dead-band” or “differential” setting. 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