{"product_id":"castair-1-2npt-f-1-2-npt-f-outlet-vent-outlet-3-8-npt-25-max-cfm-gas-engine-3-way-pilot-valve-ng-1","title":"Castair 1\/2\"NPT-F 1\/2\" NPT-F Outlet Vent Outlet 3\/8\" NPT 25 Max. CFM Gas Engine 3 Way Pilot Valve NG-1","description":"\u003ch2\u003eCastair NG-1 Three-Way Pilot Valve — 1\/2\" NPT Gas Engine, 25 CFM\u003c\/h2\u003e\n\n\u003cp\u003eThe Castair NG-1 is a three-way pilot valve built for gas engine-driven air compressor systems that operate in the 25 CFM range. It uses 1\/2\" female NPT connections on both inlet and outlet, with a 3\/8\" NPT vent port for exhaust. If your shop runs a gas-powered compressor — portable or stationary — and you need the unloader circuit to operate mechanically without relying on an electrical control signal, the NG-1 is the correct valve. The gas engine version does not use a solenoid. It responds to pneumatic pilot pressure rather than an electrical switch, which is how gas engine control systems work.\u003c\/p\u003e\n\n\u003cp\u003eThe NG-1 and NDC-1 share identical port dimensions — both use 1\/2\" female NPT inlet and outlet, 3\/8\" NPT vent. The difference is in the actuation mechanism. If you are replacing a failed valve and are not sure which version you have, look at the wiring: if there are electrical leads going to the valve body, it is the NDC-1 (electric). If the control line is purely pneumatic with no wiring, it is the NG-1 (gas engine). Installing the wrong type will cause the unloader circuit to malfunction.\u003c\/p\u003e\n\n\u003ch3\u003eWhat the NG-1 Does in the Control System\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eLoad\/Unload Cycling:\u003c\/strong\u003e The NG-1 controls when the compressor head is loaded (compressing air) and unloaded (running free). When tank pressure reaches the set point, the valve shifts and vents the unloader line, allowing the head to unload without stopping the gas engine.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMechanical Operation:\u003c\/strong\u003e Unlike electric dual valves, the NG-1 is operated by pneumatic pilot pressure — no solenoid, no electrical connection. The gas engine runs continuously, and the valve cycles the compressor head in and out of load based on pressure signal alone.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eThree-Way Function:\u003c\/strong\u003e Routes flow between three ports — inlet (from control\/tank), outlet (to unloader), and vent (exhaust on unload). The vent function is what cleanly exhausts trapped pressure from the unloader line when the compressor shifts to unloaded state.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCheck Valve Function:\u003c\/strong\u003e The three-way design prevents backflow through the pilot circuit when the compressor is in the loaded condition.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e25 CFM Capacity:\u003c\/strong\u003e Sized for mid-range compressors. Verify your compressor's actual control-circuit flow demand does not exceed 25 CFM before ordering. Undersizing the valve causes pressure drop across the valve itself, degrading control response.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003ePort Configuration and Plumbing\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eInlet:\u003c\/strong\u003e 1\/2\" female NPT — connects to the compressor discharge or tank pilot line\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOutlet:\u003c\/strong\u003e 1\/2\" female NPT — connects to the unloader mechanism on the compressor head\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eVent Outlet:\u003c\/strong\u003e 3\/8\" NPT — exhausts trapped pressure on unload; connect the Castair M38 muffler here to reduce noise\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePilot Ports:\u003c\/strong\u003e 1\/8\" female NPT — pilot pressure signal input for valve actuation\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePSI Range Options:\u003c\/strong\u003e Order NG-1100 for 100–120 PSI systems, or NG-1140 for 140–170 PSI systems. The spring and seat configuration are different between the two — using the wrong pressure range will cause early cycling or failure to unload at the set point.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eGas Engine Compressor Control — Why No Solenoid\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eEngine Runs Continuously:\u003c\/strong\u003e A gas engine-driven compressor does not stop and start with pressure like an electric motor-driven unit. The engine runs at governed RPM and the compressor head is loaded or unloaded to control air delivery.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePneumatic Signal Only:\u003c\/strong\u003e The control signal is a pneumatic pressure signal derived from the tank or discharge line. When pressure rises to the cut-out point, the pneumatic pilot signal shifts the NG-1 and the compressor head unloads.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNo Electrical Dependencies:\u003c\/strong\u003e The NG-1 has no coil, no wiring, no solenoid to fail due to moisture, voltage spikes, or vibration. For outdoor or remote-site applications where electrical reliability is a concern, this is an advantage.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDirect Comparison to NDC-1:\u003c\/strong\u003e Same port sizes, same CFM rating, same vent port size. The NG-1 is mechanically (pneumatically) actuated; the NDC-1 is solenoid (electrically) actuated. Ports are interchangeable in terms of plumbing, but the function and wiring requirements are completely different.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow a Three-Way Pilot Valve Works\u003c\/h3\u003e\n\u003cp\u003eA three-way pilot valve manages three flow paths: inlet, outlet, and exhaust. In loaded operation, the valve holds the inlet-to-outlet path open, supplying the control signal to the unloader and keeping the compressor head engaged. When the pilot pressure signal reaches the cut-out threshold, the valve spool shifts: it blocks the inlet and connects the outlet to the vent port, exhausting the unloader line pressure. This allows the unloader mechanism to open and the compressor head to run free (unloaded) while the gas engine continues running.\u003c\/p\u003e\n\n\u003cp\u003eWhen pressure in the tank drops to the cut-in threshold, the pilot signal drops and the spool shifts back to the loaded position. The vent port closes, the inlet re-pressurizes the outlet, and the unloader closes, putting the compressor back to full compression. This cycle repeats continuously during operation. The vent port must always be open to atmosphere or connected to a muffler — any back-pressure on the vent will cause delayed or failed unloading.\u003c\/p\u003e\n\n\u003ch3\u003ePilot Valve Selection Guide — Complete Castair Lineup\u003c\/h3\u003e\n\u003cp\u003eUse this table to confirm the NG-1 is correct for your application, or to identify an alternative if your system specs differ:\u003c\/p\u003e\n\n\u003ctable\u003e\n  \u003cthead\u003e\n    \u003ctr\u003e\n      \u003cth\u003ePart #\u003c\/th\u003e\n      \u003cth\u003eType\u003c\/th\u003e\n      \u003cth\u003eInlet\u003c\/th\u003e\n      \u003cth\u003eOutlet\u003c\/th\u003e\n      \u003cth\u003eVent\u003c\/th\u003e\n      \u003cth\u003eMax CFM\u003c\/th\u003e\n      \u003cth\u003eApplication\u003c\/th\u003e\n    \u003c\/tr\u003e\n  \u003c\/thead\u003e\n  \u003ctbody\u003e\n    \u003ctr\u003e\n\u003ctd\u003eD2M\u003c\/td\u003e\n\u003ctd\u003e1-way\u003c\/td\u003e\n\u003ctd\u003e1\/4\" F NPT\u003c\/td\u003e\n\u003ctd\u003eN\/A\u003c\/td\u003e\n\u003ctd\u003eDirect w\/felt\u003c\/td\u003e\n\u003ctd\u003e20\u003c\/td\u003e\n\u003ctd\u003eGas or Electric\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eBG2-M\u003c\/td\u003e\n\u003ctd\u003e2-way\u003c\/td\u003e\n\u003ctd\u003e1\/4\" F NPT\u003c\/td\u003e\n\u003ctd\u003eN\/A\u003c\/td\u003e\n\u003ctd\u003eDirect w\/felt\u003c\/td\u003e\n\u003ctd\u003e20\u003c\/td\u003e\n\u003ctd\u003eGas engine\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eBE2-M\u003c\/td\u003e\n\u003ctd\u003e2-way\u003c\/td\u003e\n\u003ctd\u003e1\/4\" F NPT\u003c\/td\u003e\n\u003ctd\u003eN\/A\u003c\/td\u003e\n\u003ctd\u003eDirect w\/felt\u003c\/td\u003e\n\u003ctd\u003e20\u003c\/td\u003e\n\u003ctd\u003eElectric dual\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eBLG\u003c\/td\u003e\n\u003ctd\u003e2-way\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/4\" F NPT pilot\u003c\/td\u003e\n\u003ctd\u003e60\u003c\/td\u003e\n\u003ctd\u003eGas engine\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eBLE\u003c\/td\u003e\n\u003ctd\u003e2-way\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/4\" F NPT pilot\u003c\/td\u003e\n\u003ctd\u003e60\u003c\/td\u003e\n\u003ctd\u003eElectric dual\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eNDC-1\u003c\/td\u003e\n\u003ctd\u003e3-way\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e3\/8\" NPT\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003eElectric dual\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003e\u003cstrong\u003eNG-1\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e3-way\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e1\/2\" F NPT\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e1\/2\" F NPT\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e3\/8\" NPT\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e25\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003eGas engine\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eNG-18\u003c\/td\u003e\n\u003ctd\u003e3-way\u003c\/td\u003e\n\u003ctd\u003e3\/4\" compression\u003c\/td\u003e\n\u003ctd\u003e1\/2\" F NPT\u003c\/td\u003e\n\u003ctd\u003e3\/8\" NPT\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003eGas engine\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eNLDC-1\u003c\/td\u003e\n\u003ctd\u003e3-way\u003c\/td\u003e\n\u003ctd\u003e3\/4\" F NPT\u003c\/td\u003e\n\u003ctd\u003e3\/4\" F NPT\u003c\/td\u003e\n\u003ctd\u003e1\/2\" NPT\u003c\/td\u003e\n\u003ctd\u003e50\u003c\/td\u003e\n\u003ctd\u003eElectric dual\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003ctd\u003eNLG-7\u003c\/td\u003e\n\u003ctd\u003e3-way\u003c\/td\u003e\n\u003ctd\u003e3\/4\" male comp.\u003c\/td\u003e\n\u003ctd\u003e3\/4\" male NPT\u003c\/td\u003e\n\u003ctd\u003e1\/2\" NPT\u003c\/td\u003e\n\u003ctd\u003e50\u003c\/td\u003e\n\u003ctd\u003eGas engine\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003cp\u003e\u003cstrong\u003ePSI Suffix:\u003c\/strong\u003e Add 100 (for 100–120 PSI) or 140 (for 140–170 PSI) to the part number. Example: NG-1100 or NG-1140. \u003cstrong\u003eMuffler:\u003c\/strong\u003e Castair M38 fits the 3\/8\" NPT vent port.\u003c\/p\u003e\n\n\u003ch3\u003eWhen Does a Shop Need the NG-1 vs. Alternatives\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNG-1 is right when:\u003c\/strong\u003e You have a gas engine-driven compressor, 1\/2\" NPT control lines, and the compressor draws 25 CFM or less through the valve. It is also the correct replacement when the original NG-1 has failed and existing plumbing is 1\/2\" NPT.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eUse NG-18 instead when:\u003c\/strong\u003e Your inlet line uses 3\/4\" compression tubing rather than 1\/2\" NPT pipe. The NG-18 has a 3\/4\" compression inlet and 1\/2\" NPT-F outlet — same CFM rating and vent size as the NG-1, just with a different inlet fitting. Gas engine application only.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eStep up to NLG-7 when:\u003c\/strong\u003e Your gas engine compressor exceeds 25 CFM at the valve, or the control lines are 3\/4\" NPT. The NLG-7 handles 50 CFM with 3\/4\" male compression inlet and 3\/4\" male NPT outlet, and a 1\/2\" NPT vent port.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eUse NDC-1 instead when:\u003c\/strong\u003e Your compressor is electric motor-driven with a dual-pressure-switch control system. The NDC-1 is the solenoid-operated equivalent — same port sizes as the NG-1, but electrically actuated.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eStep down to BG2-M when:\u003c\/strong\u003e Your gas engine system only needs a 2-way function with 1\/4\" NPT connections and 20 CFM or less. Simpler and less expensive for smaller systems.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e NG-1\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eValve Type:\u003c\/strong\u003e 3-way pilot valve\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eApplication:\u003c\/strong\u003e Gas engine-driven air compressor control systems\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOperation:\u003c\/strong\u003e Pneumatically actuated (no solenoid)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eInlet Port:\u003c\/strong\u003e 1\/2\" female NPT\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOutlet Port:\u003c\/strong\u003e 1\/2\" female NPT\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eVent Outlet Port:\u003c\/strong\u003e 3\/8\" NPT\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePilot Ports:\u003c\/strong\u003e 1\/8\" female NPT\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaximum Flow Capacity:\u003c\/strong\u003e 25 CFM\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePressure Range Options:\u003c\/strong\u003e 100–120 PSI (order as NG-1100) or 140–170 PSI (order as NG-1140)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Castair\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePrice:\u003c\/strong\u003e $115.50\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCompatible Muffler:\u003c\/strong\u003e Castair M38 (3\/8\" vent port)\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h3\u003e\n\u003cp\u003eAir Compressor Factory Direct specializes in compressor controls and replacement parts. We have stocked Castair pilot valves since 2016 and understand the gas engine vs. electric dual distinction that catches a lot of buyers off guard. When you call us, you get someone who knows why the NG-1 and NDC-1 have identical port sizes but are not interchangeable — and who will make sure you order the right valve and the right pressure range the first time.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFree Shipping:\u003c\/strong\u003e Every order ships free. No handling fees, no minimums.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFree Tech Support:\u003c\/strong\u003e Call 866-217-0063 before you order if you need help confirming part number and pressure range. We will walk through the application with you.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFull Manufacturer Warranty:\u003c\/strong\u003e Every Castair valve we sell carries the full manufacturer warranty. No grey-market parts, no refurbished valves.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCorrect Part, First Time:\u003c\/strong\u003e If you are not sure whether your system needs the NG-1 or the NG-18, or whether to order the 100 PSI or 140 PSI version, call us. We would rather spend five minutes on the phone than have you wait for a return and reorder.\u003c\/li\u003e\n\u003c\/ul\u003e\n\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":53342572511445,"sku":"NG-1","price":213.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0622\/8466\/0949\/files\/AirCompressorPilotValve_56f20fa4-6a7c-4d14-b5dc-926787b14b6d.jpg?v=1772652747","url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-1-2npt-f-1-2-npt-f-outlet-vent-outlet-3-8-npt-25-max-cfm-gas-engine-3-way-pilot-valve-ng-1","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}