HNL Pressure Switches - Selection HNL manufacture a wide range of pressure and differential pressure switches with both electrical outputs and pneumatic outputs. These include ATEX certified pressure switches suitable for use in hazardous areas. Series 100, 300 and 700 are all mechanical pressure switches - the Series 800 pressure switch is an electronic device that also functions as a pressure indicator and transmitter. All are available with aluminium or stainless steel housings and a wide selection of process wetted parts. Choose from the following list of pressure switches: Series 100 Pressure Switching only / Pneumatic output only - non-bleed two-port output switching Series 300 Pressure & Differential Pressure Switching / Compact housing / Electrical & Pneumatic outputs Series 700 - HNL's most popular pressure switch Pressure & Differential Pressure Switching / Widest selection of Ranges and Outputs / Electrical & Pneumatic outputs Series 800 Electronic Pressure & Differential Pressure Switching / Electrical output only / Indication & 4-20mA transmission Click picture for close up view Series 100 Pressure Switches (P) Series 100 Pneumatic Output Switch       Series 300 Pressure and Differential Pressure Switches (P&DP) Series 300 Standard External View. Series 300 EExd External View. Series 300 Pneumatic External View.   Series 700 Pressure and Differential Pressure Switches (P&DP) Series 700 Standard External View. Series 700 EExd External View. Series 700 Pneumatic External View.   Series 800 Pressure and Differential Pressure Switches (P&DP) Series 800 Smartstat External View     HNL Pressure Switches - Glossary Absolute Pressure Switch ATEX Bar Differential Pressure (D.P.) Switch Electrical Output Switch Hazardous Area Pneumatic Output Switch Pneumatic Pressure Switch Pressure Switch Process Connection Process Chamber Process Diaphragm Proof Pressure Range Screw Range Spring Reset Scale Plate Setpoint Switch Housing Vacuum Switch Vent Ring Wetted Parts Absolute Pressure Switch Pressure switch designed to operate at setpoints relative to absolute zero pressure. To achieve this the non-process side of the process diaphragm must be subjected to full vacuum. ATEX ATEX covers the EU directives for explosion protection in industry. ATEX gets its name from the French title of the 94/9/EC directive: Appareils destinés à être utilisés en ATmosphères EXplosibles. Bar Unit of measure for pressure. 1 bar = 1,000 mBar = 14.504 p.s.i. = 1.02 Kgf/cm2 1 bar = 100,000 Pa = 0.1 MPa 1 bar = 10.197 mH20 = 401.46 inH20 = 29.53 inHg 1 bar = 750.062 Torr = 0.987 atm Differential Pressure (D.P.) Switch A device designed to monitor two process pressures and provide an output when the difference between them reaches a set value. A mechanical D.P. switch does this by applying the two process pressure to each side of the process diaphragm to generate a force which is compared to that of a precompressed range spring. A differential pressure switch may be set to operate on either a rising D.P. (high level alarm) or a falling D.P. (low level alarm). Electrical Output Switch A single-pole double-throw (S.P.D.T.) microswitch that can be used to make or break an electrical circuit when the pressure switch operates. A microswitch with gold contacts is normally used on low voltage, low current applications (i.e. intrinsically safe circuits), and for higher voltages/currents silver contacts are used. Most microswitches have a fixed switching differential, on some it is adjustable and on others the microswitch must be manually reset with a pushbutton. Where double-pole double-throw (D.P.D.T.) switching is required it is achieved using two S.P.D.T. microswitches ganged together to operate simultaneously. By setting the two switches at different positions two switch setpoints can be achieved on the same pressure switch. Hazardous Area Area in which an explosive atmosphere exists or may exist. Explosive atmospheres may be caused by flammable gases, vapours or combustible dusts. Hazardous areas are classified into zones depending upon the likelihood of an explosive atmosphere occurring and its persistence if it does. Equipment designed for operation in hazardous areas must comply with the ATEX directive. Pneumatic Output Switch A pneumatic valve used to feed or vent a pneumatic circuit when the pressure switch operates. Pneumatic output switches can have either a fixed switching differential, an adjustable switching differential or manually reset with a pushbutton. Pneumatic Pressure Switch A pressure switch having a pneumatic output. Pressure Switch A device designed to monitor a process pressure and provide an output when a set pressure (setpoint) is reached. A mechanical pressure switch does this by applying the process pressure to a diaphragm to generate a force which is compared to that of a precompressed range spring. Process Connection Generally a tapped hole or a male thread to allow the process to be connected to the process chamber. On a pressure switch there is normally a single process connection and the switch is mounted with the process connection at the bottom. On a differential pressure switch there is a process connection on both the high and the low pressure chambers. On some very low differential pressure switches the are two process connections on each process chamber and the switch is mounted horizontally to put one connection at the top and the other at the bottom. If the process is a gas, it is connected to the upper connection and the lower connection may be used as a drain. If the process is a liquid, it is connected to the lower connection and the upper connection may be used as a vent. Threaded process connections are usually BSP.P, BSP.T or NPT. Alternative process connections include flanges and chemical seals. Process Chamber The pressure chamber that clamps the process diaphragm to the switch housing. The process chamber provides the connection(s) for the process pressure. The material from which the chamber is manufactured must be compatible with the process. Materials include anodised aluminium, PTFE, 316 stainless steel, monel, hastelloy C, etc. Process Diaphragm A thin flexible membrane in contact with the process. The process pressure acting upon the area of the diaphragm generates the force that opposes that of the range spring. The range of the switch is a function of the area of the process diaphragm and the rate of the range spring (measured in lbf/inch, N/mm etc.). The material from which the diaphragm is manufactured must be compatible with the process. Materials include nitrile rubber, viton, hastelloy C, monel, stainless steel and tantalum. Proof Pressure The design pressure of the process chamber and diaphragm and the pressure at which the switch is tested after manufacture. Maximum working pressure (M.W.P.) should be limited to 0.67 x proof pressure. Range Screw The range screw is used to adjust the setpoint of the pressure (or differential pressure) switch. It does this by changing the amount of compression on the range spring. The range screw on Series 300 and Series 700 switches is similar to a capstan and adjustment is carried out using a tommy bar supplied with the switch. Range Spring A pre-compressed spring, the force generated by this determines the pressure at which the switch operates. Reset The reset (or switching differential) is the difference in the rising and falling pressures at which the output switch operates. For a fixed differential output switch this is typically about 1% to 3% of the switch range. For an adjustable differential output switch it may be adjusted from about 5% to 12% of the switch range. Scale Plate An indicator to show the approximate setting of the pressure switch, as a percentage of the switch range. Setpoint The pressure at which the pressure switch is required to operate. A pressure switch may be set to operate on either a rising pressure (high level alarm) or a falling pressure (low level alarm). Most switches are designed to operate at a 'gauge' pressure setpoint i.e. relative to atmospheric pressure. Some applications require an 'absolute' pressure setpoint i.e. relative to absolute zero pressure, and an absolute pressure switch is required for these. Ideally the range of the switch should be chosen such that the setpoint is between 25% to 75% of this range. Switch Housing The enclosure containing the electrical or pneumatic output switch. For an electrical output one or more tapped connections (usually M20 x 1.5) are provided to allow the cable to be brought into the housing via a suitable gland. For a pneumatic output two or more bulkhead connections are provided for the output connections. Switch housings are available in either aluminium (epoxy painted) or stainless steel. Vacuum Switch Pressure switch designed to operate at pressures below atmospheric pressure (e.g. -0.5 bar gauge). This is usually achieved by including a bias spring within the process chamber which opposes the range spring (a PZ type switch). Vent Ring Isolation chamber located between the process chamber and the switch housing. Prevents the process entering the switch housing in the event of process diaphragm failure. Wetted Parts Those items within the switch that come into contact with the process (i.e. process chamber and diaphragm etc.). The materials of wetted parts must be chosen to be compatible with the process media. Thank you for visiting the HNL website, please contact us if you require any further information.