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91430 SPS cover edited - Electronic Fasteners Inc

91430 SPS cover edited - Electronic Fasteners Inc

PRESSURE PLUGS

PRESSURE PLUGS Application DataPressure plugs are not pipe plugs.Pipe plugs (plumber’s fittings) arelimited to pressures of 600 psi, aresealed with a compound, and aremade of cast iron with cut threadsand protruding square drive.Pressure plugs are made tocloser tolerances, are generally ofhigher quality, and almost all havetaper threads. Properly made andused, they will seal at pressures to5000 psi and without a sealing compound(pressure tests are usually at20,000 psi.) they are often used inhydraulic and pneumatic designs.Performance RequirementsPressure plugs used in industrialapplications should: not leak at pressures to 5000 psi need no sealing compounds be reusable without seizure give a good seal when reused seal low viscosity fluids require minimum seating torque require minimum re-tooling orspecial tools.For a satisfactory seal, the threads ofthe plug and those in the mating holemust not gall or seize up to maximumpossible tightening torque. Gallingand seizure are caused by metalpickup on the mating surfaces andare directly related to force on thesurface, material hardness, lubricationused, and thread finish.How Pressure Plugs SealSealing is achieved by crushing thecrest of one thread against the rootof the mating thread. If too muchof compressive force is required totorque the plug, it will tend to gallin the hole. Too little force will notdeform the crest of threads enoughto produce a seal. Increasing thehardness of the material will reducegalling but will also increase therequired sealing force. Generally ahardness range of Rc 30 to 40 willmeet most requirements. The tighteningforce must be low enough tocause no galling in this range.Cost ConsiderationsDryseal plugs are more frequentlyused, especially where reuse is frequent.Reason: more threads areengaged and they therefore resistleakage better. They are also preferredin soft metals to reduce ofover-torquing.TYPES OF PRESSUREPLUG THREADSThree thread forms are commonlyused for pipe plugs and pressureplugs:NPT: National Pipe thread, Tapered.This is the thread form commonlyused for commercial pipe and fittingsfor low pressure applications. A lubricantand sealer are generally used.ANPT: Aeronautical National Pipethread, Tapered. Covered by MIL-S-7105, this thread form was developedfor aircraft use. It is basically thesame as the NPT thread except thattolerances have been reduced about50 percent. Plugs made with thisthread should be used with lubricantsand sealers. They are not to be usedfor hydraulic applications.NPTF: National Pipe thread, Tapered,Fuel. This is the standard thread forpressure plugs. They make pressuretightjoints without a sealant.Tolerances are about 1/4 those forNPT threads. The standard whichapplies is ANSI B1.20.3. Applicablefor fluid power applications.APPLICATION DATA – DRYSEAL TYPEthreads tap tap recommendednom. per drill drill torquesize inch size+ size ++ in.-lbs*1/16 27 15/64 1/4 1501/8 27 21/64 11/32 2501/4 18 27/64 7/16 6003/8 18 9/16 37/64 12001/2 14 11/16 23/32 18003/4 14 57/64 59/64 30001 11 1/2 1 1/8 1 5/32 42001 1/4 11 1/2 37.5mm – 54001 1/2 11 1/2 43.5mm – 69002 11 1/2 2 3/16 – 8500Unbrako recommends using a tapered reamer with correspondingsize tap drill (see page 27).+With use of reamer (taper thread).++Without use of tapered reamer.*Recommended torques for alloy steel only. Multiply by .65 forstainless steel and .50 for brass.NPTF fully formed Dryseal threads achieve seal in tapped holeswithout need for sealing compounds.26

PRESSURE PLUGSPTFE/TEFLON-Coated LEVL-SEAL Type Dryseal Thread Form with 7/8-inch Taper per FootDeliberate difference in taper betweenthe plug and the tapped hole. Idealfor use in assemblies where clearanceis limited and in hydraulic lines nearmoving parts. Designed for use inhard materials and in thick-walledsections as well as for normal plugapplications.internal root crushesNPTF external crest hereINTERNAL THREADS(HOLE)PLUGexternal root crushesinternal crest hereHigh pressure seal – Achievedthrough metal-to-metal contact at thelarge end of the plug. High loadplaced on the few mating threadsnear the top of the hole.Flush seating – Design of LEVL-SEALplug permits seating within half apitch in a normally tapped hole.Conventional plugs have the greatertolerance of a full pitch and usuallyprotrude above the surface.PTF fully formed Dryseal threadsdesigned to achieve seal in tappedholes without need for sealing compounds.PTFE/TEFLON CoatedLEVL-SEAL TypeTypical thickness is 0.0005-inchLEVL-SEAL precision coated withtough, corrosion-resistantPTFE/TEFLON.Installation of the new plugs is fasterwith the coating of PTFE/TEFLONwhich acts as a lubricant as well asseal. Power equipment can be usedto install the smaller sizes instead ofthe manual wrenching required byhigher torques of uncoated plugs.Suited for in assembly line production.Higher hydraulic and pneumaticworking pressures can be effectivelysealed. Seal is effective without useof tapes or sealing compounds, evenwith liquids of very low viscosity.SPS Laboratories have tested theseplugs with surges up to 13,500 psi 8times in 5 minutes, then held peakpressure for 6 full hours without traceof leakage.Flush seating improves appearanceand adds safety. LEVL-SEALplugs seat flush because of a combinationof (1) gaging procedures, and(2) a deliberate difference in taperbetween the plug and a normallytapped NPTF hole. (The taper of theplug is 7/8” per foot , while that of thehole is 3/4” per foot.)PTFE/TEFLON was selected forthe coating material because of itscombination of extra hardness andabrasion resistance which permitreuse up to 5 times without appreciableloss of seal.The coating is serviceable to+450°F without deterioration.Temperatures lower than –100°Frequire the use of stainless steel plugs.These are available in the same rangeof sizes as the alloy steel plugs.With no tape or sealing compoundinvolved, there is no danger of foreignmatter entering and contaminatingthe system or equipment. The coatingreduces any tendency of the plug to“freeze” in the hole because of rustor corrosion.APPLICATION DATA – LEVL-SEAL and LEVL-SEAL with PTFE/TEFLONrecommended hole diametertapping informationimperfectrecommendednom.threadstap projection thru L 1 ringthreads tap* drill torque (inch-lbs.)size per inch max. min. max. min. allowable size alloy steel**1/16 27 .2374 .2334 .375 .250 4 15/64 1501/8 27 .3311 .3271 .375 .250 4 21/64 2501/4 18 .4249 .4209 .521 .397 4 27/64 6003/8 18 .5655 .5615 .516 .392 4 9/16 12001/2 14 .6905 .6865 .641 .517 4 11/16 18003/4 14 .8936 .8896 .627 .503 4 57/64 30001 11 1/2 1.1280 1.1240 .772 .584 4 1 1/8 42001 1/4 11 1/2 1.4794 1.4754 .780 .592 4 37.5mm 54001 1/2 11 1/2 1.7165 1.7116 .793 .605 4 43.5mm 69002 11 1/2 2.1905 2.8165 .761 .573 4 2 3/16 8500*For taper thread (using tapered reamer). For tap drill size(without using tapered reamer) see table and correspondingcomment on page 26.**Maximum for PTFE/TEFLON-coated but can be reduced asmuch as 60% in most applications.27

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