What is the difference between NW, QF, KF and ISO vacuum fittings?
There is none. Click here for dimensions to determine sizes. The PDF which comes up on the screen, or should, can then be printed and is "to scale" meaning you simply place your part (the flange) over it and you should be able to ascertain what NW size you are looking for. Another description is offered off the main home page.
What is the term NPT, MNPT and FNPT?
NPT is defined as National Pipe Thread. This is a standard tapered thread fitting you can purchase at most hardware or plumbing supply stores locally. If you are making long vacuum line runs you can purchase black pipe (carbon steel), aluminum pipe, stainless steel and even use plastic PVC piping that is joined and sealed correctly, terminating with male or female NPT fittings that can transition to the system vacuum fittings. NPT fittings come in 2 styles, Male or MNPT and Female or FNPT (see link above). Since these fitting threads are tapered, some knoledge and care need to be made when assessing and measuring the fitting to get the correct NPT size. Use of a vacuum sealant is required to get a leak free joint from fitting to fitting. Teflon tape IS NOT recommended or used in the vacuum industry. A "tight" leak free seal is desired.
You have different types of Orings like Buna-N, Viton, Silicone and EPDM. Why?
These are the most common rubber or elastomeric compounds. There are also very exotic and very expensive o'rings like Chemraz, Kalraz, Teflon in various flavors. The variations have certain properties that are desired for very demanding applications. They can be highly expensive. Buna-N is the least expensive and has good resistance to things like vacuum pump oils. Viton has very good broad spectrum chemical resistance. Silicone is used in Oxygen rich systems where hydrocarbons are not allowed. Much of the selection process is a result of understanding the chemistry in the vacuum system. Some are better than others depending on what specifically is expected to be present and application. Since it is often difficult to determine one black O'ring from another, we mark ours to make it simple for you. Buna-N is black. Viton is black with a green stripe for identification at your location. EPDM we stripe yellow. Silicone is an orange-ish brown color, not black. Teflon is white. If they are from us, you won't need to guess.
You have different materials of construction? Fittings in stainless, aluminum, brass and plastic. Why?
Usually 6061 aluminum is the least expensive but not as durable as say stainless. 304 Stainless steel has high, broad spectrum, chemical resistance and is very durable. Plastic can be manufactured in Ryton, PVC and many other compounds. PVC is fairly resistant to chemical degradation but plastic variations need to be considered in high vacuum applications for potential porosity and out gassing issues. Brass is used a lot in the HVAC industry like air conditioning systems. We cut all these materials and can easily use alternatives with demand and a quantity order. If you are cobbling together a system that is pretty much once and done, then aluminum or plastic can be a good choice. If you are taking the system apart regularly, it is "out in the field", or the chemistry gets complicated then probably durable stainless is the better choice.
Will you make "custom" fittings?
Sure, love to, but you must understand that this can get to be an expensive process. If we are "running" NW25 x XXXX fittings and you want some custom NW25 sizes then OK. If you want 1, then it gets pricey. If you want 50 or 100 then we can talk. There are some large up front costs on a special and the costs need to be amortized over the quantity produced in the run. Generally up front costs are the "engineering" costs and programming costs, maybe setup and potentially tooling costs if the alloy desired gets really special.
I don't see what I want??? Well, Call us 800-628-0850 and we will see if we can help.
We did not feature everything we have, tried to, but probably didn't due to the very specific nature of some of the parts. We can also supply Conflat parts of most configurations. Large flange and ASA parts also. We make a lot of crazy stuff that other people do not. We like having one of the broadest and most complete product offerings of these parts around.
What pressure do these NW fittings support?
Generically speaking due to the use of oring seals these fittings can be considered for use to 10-6 Torr or .000001 Torr or .000001 mm Mercury vacuum (Hg). Much higher vacuum pressures like 10-8 or 10-10 Torr often require metal to metal seals and we have these available. They are termed Conflat or ASA flanges and are used on real "ultra high" vacuum systems. How much "positive" pressure? Not much. These are designed and engineered for negative pressures (if you can think of pressure as negative). So 15 psi positive pressure maximum and even then, the use of over pressure ring fittings on the joint with the clamp should be considered.
Where do you stock these?
Right outside of Philadelphia on the East Coast of the USA we have a factory that produces the majority of these fittings on CNC machines (computer numerically controlled). We do import some things. Standard ground shipping is readily available on a daily basis as is expedited services. We inventory these various items based on historic demands and such. We usually ship off the shelf but Murphy's Law can play a part and someone comes in and orders 100 widgets and we have 105, then we ship off the shelf and adjust the machining schedule for restock. The next order for 20 would obviously have to wait for the schedule. We try and prioritize the schedule for common sizes. We would call ASAP and notify the order placement location of the current status at time of order, anticipated delivery date if not immediate or stock is short.
How are these fittings constructed?
We machine the vast majority of these fittings out of solid metal bars or extruded plastic bar stock. There are welded fittings in the product line also but we do not involve welding on parts we can machine. Other people use welds to make say a hose fittings or MNPT fittings. It is less expensive but we don't do that. A weld is a potential leak and we like our machines to run. Instrument fittings, Tees, Elbows and Crosses as an example are welded. Welded fittings have the potential for "leaks" at the weld. We try and maintain superior quality in this area, but no one is perfect. If desired we can leak test them using a few methods. Leak detection certifications using a helium mass spectrometer prior to shipping would be an added cost but the service is available.
Are these fittings cleaned for pure oxygen and other demanding service?
Cleaning these parts can be discussed if you have special desires. Generally speaking we machine them using a "coolant" referred to as 95/5 in the oil business or 95% water and 5% coolant. Once the parts come off the CNC machines they are blown off/dry with compressed air, we then immerse them immediately in a water bath to remove any coolant "drag out" or drops of coolant remaining on the part. So the 5% coolant gets reduced to close to zero or something pretty small. We recently invested in some ultrasonic cleaning tanks which is where a batch of parts will go before finally going on the shelf. We are not a "white room" facility, we are a factory and there is stuff, dust and all, that floats around and can get on the parts. We are in process of pushing everything on the shelf through the ultrasonic cleaners and then re-bagging for the shelf. This is our standard procedure and where we are now on the cleaning process.
Back to the original question. Cleaning to a specification. We have a number of outside companies locally that will clean prep these things for Oxygen service, Mil-Spec service, Fed-Spec or any other demanding service. Please understand these are outside services and change the price and lead times accordingly. Can we do it? Sure. Can you wait and accept the change in price for this service. The market will tell. Will they then be certified? Of course, the outside service will provide the required documentation.