THE BASICS OF PRESSURE REGULATORS
THE BASICS OF PRESSURE REGULATORSContentsThe Basics of Pressure RegulatorsMaterialFluid used (gas, liquid, toxic or flammable)TemperatureOperating PressuresFlow RequirementsSize & WeightPressure Reducing Element (poppet valve)Sensing Element (piston or diaphragm)The Reference Force Element (spring)Regulator Accuracy and CapacityDroop DefinitionOrifice SizeLock Up PressureHysteresisPressure regulators are found in many common home andindustrial applications. For example, pressure regulators areused in gas grills to regulate propane, in home heating furnaces toregulate natural gas, in medical and dental equipment to regulateoxygen and anesthesia gases, in pneumatic automation systemsto regulate compressed air, in engines to regulate fuel and in fuelcells to regulate hydrogen. As this partial list demonstrates thereare numerous applications for regulators yet, in each of them, thepressure regulator provides the same function. Pressure regulatorsreduce a supply (or inlet) pressure to a lower outlet pressure andwork to maintain this outlet pressure despite fluctuations in theinlet pressure. The reduction of the inlet pressure to a lower outletpressure is the key characteristic of pressure regulators.When choosing a pressure regulator many factors must beconsidered. Important considerations include: operating pressureranges for the inlet and outlet, flow requirements, the fluid (Is it agas, a liquid, toxic, or flammable?), expected operating temperaturerange, material selection for the regulator components includingseals, as well as size and weight constraints.Single-Stage RegulatorTwo-Stage (Dual Stage) RegulatorThree-Stage RegulatorInstallation GuideBeswick pressure regulators can beviewed at http://catalog.beswick.comPRD2-2N2PR2Excellence in Miniaturebeswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
THE BASICS OF PRESSURE REGULATORSMATERIALSA wide range of materials are available to handlevarious fluids and operating environments. Commonregulator component materials include brass, plastic,and aluminum. Various grades of stainless steel (suchas 303, 304, and 316) are available too. Springs usedinside the regulator are typically made of music wire(carbon steel) or stainless steel.Brass is suited to most common applications and isusually economical. Aluminum is often specified whenweight is a consideration. Plastic is considered whenlow cost is of primarily concern or a throw away itemis required. Stainless Steels are often chosen for usewith corrosive fluids, use in corrosive environments,when cleanliness of the fluid is a consideration orwhen the operating temperatures will be high.Equally important is the compatibility of the sealmaterial with the fluid and with the operatingtemperature range. Buna-n is a typical seal material.Optional seals are offered by some manufacturers andthese include: Fluorocarbon, EPDM, Silicone, andPerfluoroelastomer.FLUID USED - (GAS, LIQUID, TOXIC,or FLAMMABLE)The chemical properties of the fluid should beconsidered before determining the best materials foryour application. Each fluid will have its own uniquecharacteristics so care must be taken to select theappropriate body and seal materials that will comein contact with the fluid. The parts of the regulatorin contact with the fluid are known as the “wetted”components.It is also important to determine if the fluid isflammable, toxic, explosive, or hazardous in nature.A non-relieving regulator is preferred for use withhazardous, explosive, or expensive gases becausethe design does not vent excessive downstreampressure into the atmosphere. In contrast to anon-relieving regulator, a relieving (also known asself-relieving) regulator is designed to vent excessdownstream pressure to atmosphere. Typically thereis a vent hole in the side of the regulator body for thispurpose. In some special designs, the vent port canbe threaded and any excess pressure can be ventedfrom the regulator body through tubing and exhaustedin a safe area. If this type of design is selected theexcess fluid should be vented appropriately and inaccordance to all safety regulations.TEMPERATUREOPERATING PRESSURESThe materials selected for the pressure regulator notonly need to be compatible with the fluid but also mustbe able to function properly at the expected operatingtemperature. The primary concern is whether or notthe elastomer chosen will function properly throughoutthe expected temperature range. Additionally, theoperating temperature may affect flow capacity and/orthe spring rate in extreme applications.The inlet and outlet pressures are important factors toconsider before choosing the best regulator. Importantquestions to answer are: What is the range offluctuation in the inlet pressure? What is the requiredoutlet pressure? What is the allowable variation inoutlet pressure?FLOW REQUIREMENTSSIZE & WEIGHTWhat is the maximum flow rate that the applicationrequires? How much does the flow rate vary? Portingrequirements are also an important consideration.In many high technology applications space islimited and weight is a factor. Some manufacturesspecialize in miniature components and should beconsulted. Material selection, particularly the regulatorbody components, will impact weight. Also carefullyconsider the port (thread) sizes, adjustment styles,and mounting options as these will influence size andweight.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
PRESSURE REGULATORS IN OPERATIONA pressure regulator is comprised of three functionalelements:1.) A pressure reducing or restrictive element. Often thisis a spring loaded poppet valve.2.) A sensing element Typically a diaphragm or piston.3.) A reference force element. Most commonly a spring.In operation, the reference force generated by the springopens the valve. The opening of the valve appliespressure to the sensing element which in turn closesthe valve until it is open just enough to maintain the setpressure. The simplified schematic “Pressure RegulatorSchematic” illustrates this force balance arrangement.(1) PRESSURE REDUCING ELEMENT(poppet valve)Most commonly, regulators employ a spring loaded“poppet” valve as a restrictive element. The poppetincludes an elastomeric seal or, in some high pressuredesigns a thermoplastic seal, which is configured to makea seal on a valve seat. When the spring force movesthe seal away from the valve seat, fluid is allowed toflow from the inlet of the regulator to the outlet. As theoutlet pressure rises, the force generated by the sensingelement resists the force of the spring and the valve isclosed. These two forces reach a balance point at the setpoint of the pressure regulator. When the downstreampressure drops below the set-point, the spring pushes thepoppet away from the valve seat and additional fluid isallowed to flow from the inlet to the outlet until the forcebalance is restored.(2) SENSING ELEMENT (piston ordiaphragm)Piston style designs are often used when higher outletpressures are required, when ruggedness is a concernor when the outlet pressure does not have to be held toa tight tolerance. Piston designs tend to be sluggish, ascompared to diaphragm designs, because of the frictionbetween the piston seal and the regulator body.In low pressure applications, or when high accuracy isrequired, the diaphragm style is preferred. Diaphragmregulators employ a thin disc shaped element which isused to sense pressure changes. They are usually madeof an elastomer, however, thin convoluted metal is usedin special applications. Diaphragms essentially eliminatethe friction inherent with piston style designs. Additionally,for a particular regulator size, it is often possible toprovide a greater sensing area with a diaphragm designthan would be feasible with a piston style design.(3) THE REFERENCE FORCE ELEMENT(spring)The reference force element is usually a mechanicalspring. This spring exerts a force on the sensing elementand acts to open the valve. Most regulators are designedwith an adjustment which allows the user to adjust theoutlet pressure set-point by changing the force exerted bythe reference spring.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
PRESSURE REGULATORS IN OPERATIONREGULATOR ACCURACY ANDCAPACITYThe accuracy of a pressure regulator is determined bycharting outlet pressure versus flow rate. The resultinggraph shows the drop in outlet pressure as the flowrate increases. This phenomenon is known as droop.Pressure regulator accuracy is defined as how muchdroop the device exhibits over a range of flows; lessdroop equals greater accuracy. The pressure versus flowcurves provided in the graph “Direct ActingPressure Regulator Operating Map”, indicates the usefulregulating capacity of the regulator. When selecting aregulator, engineers should examine pressure versus flowcurves to ensure the regulator can meet the performancerequirements necessary for the proposed application.DROOP DEFINITIONHYSTERESISHysteresis can occur in mechanical systems, such aspressure regulators, due to friction forces caused bysprings and seals. Take a look at the graph and youwill notice, for a given flow rate, that the outlet pressurewill be higher with decreasing flow than it will be withincreasing flow.LOCK UP PRESSURE“Lockup pressure” is the pressure above the set-pointthat is required to completely shut the regulator valve offand insure that there is no flow.The term “droop” is used to describe the drop in the outletpressure, below the original set-point, as flow increases.Droop can also be caused by significant changes in theinlet pressure (from the value when the regulator outputwas set). As the inlet pressure rises from the initialsetting, the outlet pressure falls. Conversely, as the inletpressure falls, the outlet pressure rises. As seen in thegraph “Direct Acting Pressure Regulator Operating Map”,this effect is important to a user because it shows theuseful regulating capacity of a regulator.ORIFICE SIZEIncreasing the valve orifice can increase the flow capacityof the regulator. This may be beneficial if your design canaccommodate a bigger regulator however be careful notto over specify. A regulator with an oversized valve, forthe conditions of the intended application, will result in agreater sensitivity to fluctuating inlet pressures, and maycause excessive droop.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
SINGLE, TWO, & THREE STAGE REGULATORSSINGLE-STAGE REGULATORPRPRD-2N2TWO-STAGE (DUAL-STAGE) REGULATORA two-stage pressure regulator is ideal for applications with largevariations in the flow rate, significant fluctuations in the inletpressure, or decreasing inlet pressure such as occurs with gassupplied from a small storage tank or gas cylinder.With most single-stage regulator regulators, except thosethat use a pressure compensated design, a large drop in inletpressure will cause a slight increase in outlet pressure. Thishappens because the forces acting on the valve change, due tothe large drop in pressure, from when the outlet pressure wasinitially set. In a two-stage design the second stage will notbe subjected to these large changes in inlet pressure, only theslight change from the outlet of the first stage. This arrangementresults in a stable outlet pressure from the second stage despitethe significant changes in pressure supplied to the first stage.Single-stage regulators are an excellent choice forrelatively small reductions in pressure. For example, theair compressors used in most factories generate maximumpressures in the 100 to 150 psi range. This pressure is pipedthrough the factory but is often reduced with a single-stageregulator to lower pressures (10 psi, 50 psi, 80 psi etc.) tooperate automated machinery, test stands, machine tools, leaktest equipment, linear actuators, and other devices. Singlestage pressure regulators typically do not perform well withlarge swings in inlet pressure and/or flow rates.BESWICK ADVANTAGE: 100% TESTEDWe take the time to functionally test 100% of ourregulators before shipping to ensure that youreceive the highest quality product.PR2PRD2-3N1THREE-STAGE REGULATORPRD3HPA three-stage regulator provides a stable outlet pressure similarto a two-stage regulator but with the added ability to handle asignificantly higher maximum inlet pressure. For example, theBeswick PRD3HP series three-stage regulator is rated to handlean inlet pressure as high as 3,000 psi and it will provide a stableoutlet pressure (in the 0 to 30 psi range) despite changes to thesupply pressure. A small and lightweight pressure regulatorthat can maintain a stable low output pressure, despite an inletpressure that will decrease over time from a high pressure, is acritical component in many designs. Examples include portableanalytical instruments, hydrogen fuel cells, UAVs, and medicaldevices powered by high pressure gas supplied from a gascartridge or storage cylinder.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
INSTALLATION GUIDENow that you have chosen the regulator thatbest suits your application it is important that theregulator is installed and adjusted properly to insurethat it functions as intended.Most manufacturers recommend the installation ofa filter upstream of the regulator (some regulatorshave a built-in filter) to prevent dirt and particulatesfrom contaminating the valve seat. Operation of aregulator without a filter could result in fluid leakingto the outlet port if the valve seat is contaminatedwith dirt or foreign material. Regulated gasesshould be free from oils, greases, and othercontaminants which could foul or damage the valvecomponents or attack the regulator seals. Manyusers are unaware that gases supplied in cylindersand small gas cartridges can contain traces of oilsfrom the manufacturing process. The presence ofoil in the gas is often not apparent to the user andtherefore this topic should be discussed with yourgas supplier before you select the seal materials foryour regulator. Additionally, gasses should be freeof excessive moisture. In high flow rate applications,icing of the regulator can occur if moisture ispresent.If the pressure regulator will be used with oxygen,be aware that that oxygen requires specializedknowledge for safe system design. Oxygencompatible lubricants must be specified and extracleaning, to remove traces of petroleum basedcutting oils, is typically specified. Make certain thatyou inform your regulator supplier that you plan touse the regulator in an oxygen application.Do not connect regulators to a supply source witha maximum pressure greater than the rated inletpressure of the regulator. Pressure regulators arenot intended to be used as shutoff devices. Whenthe regulator is not in use, the supply pressureshould be turned off.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
INSTALLATION GUIDESTEP 1Begin by connecting the pressure source to the inlet port and the regulated pressure line to the outlet port.If the ports are not marked, check with the manufacturer to avoid incorrect connections. In some designs,damage can occur to the internal components if the supply pressure is mistakenly supplied to the outletport.STEP 2Before turning on the supply pressure to the regulator, back off the adjustment control knob to restrictflow through the regulator. Gradually turn on the supply pressure so as not to “shock” the regulator with asudden rush of pressurized fluid. NOTE: Avoid turning the adjustment screw all the way into the regulatorbecause, in some regulator designs, the full supply pressure will be delivered to the outlet port.STEP 3Set the pressure regulator to the desired outlet pressure. If the regulator is non-relieving, it will be easierto adjust the outlet pressure if fluid is flowing rather than “dead ended” (no flow). If the measured outletpressure exceeds the desired outlet pressure, vent the fluid from the downstream side of the regulator andlower the outlet pressure by turning the adjustment knob. Never vent fluid by loosening fittings, as injurymay result.With a relieving style regulator, excess pressure will be automatically vented to atmosphere from thedownstream side of the regulator when the knob is rotated to lower the output setting. For this reason, donot use relieving style regulators with flammable or hazardous fluids. Be sure the excess fluid is ventedsafely and in accordance with all local, state and federal regulations.STEP 4To obtain the desired outlet pressure, make the final adjustments by slowly increasing the pressure frombelow the desired set point. Setting the pressure from below the desired setting is preferred to setting itfrom above the desired setting. If you overshoot the set point while setting the pressure regulator, backoff the set pressure to a point below the set point. Then, again, gradually increase the pressure to thedesired set point.STEP 5Cycle the supply pressure on and off several times while monitoring the outlet pressure to confirm theregulator is consistently returning to the set point. Additionally, the outlet pressure should also be cycledon and off to ensure the pressure regulator returns to the desired set point. Repeat the pressure settingsequence if the outlet pressure does not return to the desired setting.beswick engineering co., inc. Miniature Fluid Power Products284 Ocean Rd. Greenland, NH 03840-2442 603-433-1188www.beswick.com
reduce a supply (or inlet) pressure to a lower outlet pressure and work to maintain this outlet pressure despite luctuations in the inlet pressure. The reduction of the inlet pressure to a lower outlet pressure is the key characteristic of pressure regulators. When choosing a pre
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