{"product_id":"castair-pressure-switch-145-175-psi-on-off-w-unloader-on-off-psh1mix","title":"Castair Pressure Switch 145-175 PSI On\/Off w\/unloader \u0026 on\/off PSH1MIX","description":"\u003cp\u003eThe Castair PSH1MIX is a 145-175 PSI pressure switch with an integral unloader valve and on\/off control. At $40.73, it is the direct upgrade from the PSH1 (no-unloader version) and is the correct choice when the compressor motor needs the line pressure vented at shutdown to enable reliable restart. The unloader valve in the PSH1MIX opens when the compressor reaches cut-out pressure (175 PSI), releasing the pressure trapped in the pump head and outlet line — so when the motor restarts at cut-in (145 PSI), it starts against much lower back-pressure and has an easier time getting up to speed.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eNote: Cast Air did not provide a dedicated manufacturer product page for this switch.\u003c\/strong\u003e Specifications are drawn from the product listing. Contact us to confirm electrical rating and full compatibility with your compressor model before ordering.\u003c\/p\u003e\n\n\u003ch2\u003eWhy the Unloader Valve Matters\u003c\/h2\u003e\n\u003cp\u003eWhen a piston compressor motor stops at cut-out pressure, compressed air remains in the cylinder head and the outlet line between the check valve and the motor outlet. This trapped air creates back-pressure that the motor must overcome when it restarts. For motors with high starting torque (capacitor-start designs with strong start windings), this is manageable. For motors with weaker starting characteristics — or motors running near their nameplate amperage limit — starting against residual head pressure causes:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eSlow or failed start (motor hums, does not reach operating speed)\u003c\/li\u003e\n\u003cli\u003eOverload protector trips on the motor\u003c\/li\u003e\n\u003cli\u003eExcessive inrush current that trips breakers or damages motor windings over time\u003c\/li\u003e\n\u003cli\u003ePremature motor failure from repeated locked-rotor current events\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe unloader valve in the PSH1MIX solves this by bleeding off the head pressure the moment the compressor stops. At the next start cycle, the motor starts against essentially atmospheric pressure — its easiest possible load condition.\u003c\/p\u003e\n\n\u003ch3\u003eSwitch Specification Details\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e PSH1MIX\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePressure Range:\u003c\/strong\u003e 145-175 PSI (cut-in 145 PSI \/ cut-out 175 PSI)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eControl Type:\u003c\/strong\u003e On\/Off\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUnloader:\u003c\/strong\u003e Yes — integral unloader valve included\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eApplication:\u003c\/strong\u003e Cast Air single-stage compressors where unloader is required for reliable motor restart\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrice:\u003c\/strong\u003e $40.73\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eHow the Integral Unloader Works\u003c\/h2\u003e\n\u003cp\u003eThe PSH1MIX combines the pressure switch contacts and the unloader valve in a single assembly. Here is the operating sequence:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eTank pressure reaches 175 PSI cut-out → switch contacts open → motor stops → unloader valve opens → head pressure vents to atmosphere\u003c\/li\u003e\n\u003cli\u003eTank pressure drops to 145 PSI cut-in → switch contacts close → motor starts against vented (low back-pressure) head → compressor pumps air into tank\u003c\/li\u003e\n\u003cli\u003eTank pressure reaches 175 PSI cut-out → cycle repeats\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe unloader vent is typically plumbed to the pump head or the outlet line between the pump and the check valve. Confirm the unloader port connection for your specific Cast Air compressor before installing.\u003c\/p\u003e\n\n\u003ch2\u003ePSH1MIX vs. PSH1 — When to Use Each\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eUse PSH1MIX (this switch)\u003c\/strong\u003e when: motor struggles to restart, overload protector trips repeatedly at restart, breaker trips on startup, or when replacing a failed switch that originally had an unloader\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUse PSH1 (no unloader)\u003c\/strong\u003e when: the compressor uses a separate unloader mechanism, the motor restarts reliably without an unloader, or the system design specifically calls for no unloader in the pressure switch\u003c\/li\u003e\n\u003cli\u003eIf you are not sure which is correct for your compressor, call us — we can identify the right switch based on the compressor model and motor type\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eWhen Does a Shop Need the PSH1MIX?\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003ePressure switch has failed and the original switch had an integral unloader\u003c\/li\u003e\n\u003cli\u003eMotor is struggling to restart, tripping overload, or slow to start after stopping at pressure\u003c\/li\u003e\n\u003cli\u003eUpgrading from PSH1 (no unloader) because of motor restart issues\u003c\/li\u003e\n\u003cli\u003eReplacing a corroded or mechanically failed pressure switch\/unloader assembly on a Cast Air high-pressure unit\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e PSH1MIX\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Cast Air (Castair)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCut-In Pressure:\u003c\/strong\u003e 145 PSI\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCut-Out Pressure:\u003c\/strong\u003e 175 PSI\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDifferential:\u003c\/strong\u003e 30 PSI\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUnloader:\u003c\/strong\u003e Yes — integral\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eControl:\u003c\/strong\u003e On\/Off\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eElectrical Rating:\u003c\/strong\u003e Not confirmed in listing — call to verify voltage and amperage rating for your motor\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrice:\u003c\/strong\u003e $40.73\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Data:\u003c\/strong\u003e Product page not available — specifications from product listing data\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eWhat Is Included\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e1x Castair PSH1MIX pressure switch with integral unloader valve\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eUnloader tubing and fittings for plumbing to the pump head are not included. Confirm the unloader port connection type before installing. Always de-energize and depressurize the system completely before replacing a pressure switch.\u003c\/p\u003e\n\n\u003ch2\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h2\u003e\n\u003cp\u003eWe stock both the PSH1 and PSH1MIX and can help you determine which is correct for your specific Cast Air compressor. If your motor is struggling to restart, the PSH1MIX is almost always the right answer — and at only $4.42 more than the PSH1, the unloader is a minimal cost for the protection it provides. Free shipping on all orders, free tech support, full manufacturer warranty since 2016.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eCast Air specialist\u003c\/strong\u003e since 2016\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFree shipping\u003c\/strong\u003e on all orders\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFree tech support\u003c\/strong\u003e — we determine whether PSH1 or PSH1MIX is correct for your application\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eFull manufacturer warranty\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHonest guidance\u003c\/strong\u003e — we will tell you if the no-unloader PSH1 is actually sufficient\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cstrong\u003eCall 866-217-0063 for quick answers and help!\u003c\/strong\u003e\u003c\/p\u003e","brand":"Cast Air","offers":[{"title":"Default Title","offer_id":53342574739669,"sku":"PSH1MIX","price":75.26,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0622\/8466\/0949\/files\/PRESSURE-SWITCHES.jpg?v=1772652798","url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-pressure-switch-145-175-psi-on-off-w-unloader-on-off-psh1mix","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}