Planning
Frequently Asked Questions
This list of questions was developed by listening to customers just like you when they asked, “Why didn’t I know that?” Before you order devices, build your fixture or even consider your design complete, we suggest you run through this checklist to check for some common problems. Should I use or at least consider using double acting cylinders? Double acting cylinders will assure full cylinder retraction on a timely basis even in systems where restrictions such as small orifices or long tubing runs have been introduced. The use of double acting cylinders is especially important if “return” time is critical (as in some CNC systems). We also recommend use of double acting cylinders in systems operating below 800 psi. Note: Minimum operating pressure for Vektek single acting devices is 750 psi and for double acting devices is 500 psi. If single acting cylinders must be used: Have I reduced the number of fittings (orifices), length of tubing and restrictions as much as possible? Are all of these properly sized? Some fittings and hoses which are locally available (not from Vektek) have extremely small orifices which restrict flow. The use of 1/8 or similar size fittings can have this effect on a system. This restriction is even more pronounced when introduced at a main feed line. This can happen with some fittings and many hoses. Excessive tubing length can create a “column” of oil which is very long. Friction created by moving oil through tubing and hose will slow response times because of the inertia of the column of oil and increased backpressure of returning oil. If single acting springs are all that is pushing this oil, it is possible that this backpressure can become sufficient to stall the cylinder. Proper sizing of fittings for main feed lines and device supply lines will normally be accomplished by using the appropriate VektorFlo ® fluid distribution manifold. Device lines are Size-4 (1/4 OD which match to fit SAE 4 ports and adapt to the occasional use of SAE 2). Main feed lines are Size-6 (3/8 OD, SAE 6). The use of smaller lines Size-2 (1/8) for devices or Size-4 (1/4) for feed lines may cause excessive restrictions. Normally, avoid using an SAE 4 quick disconnect to feed an entire fixture.
against a fixed stop. In order to machine “into” a clamp, the clamp must be sufficiently sized to resist all cutter and machine forces or the part will tend to shift. When I use a dial indicator on my part, it bends when it is clamped. Why? Clamps should be positioned directly opposite a fixed locator, hydraulic support or other supporting element. This element may be a part of the fixture, a solid portion of a rigid part or a properly sized floating locator such as a hydraulic work support. If your clamp is putting force into your part which is not transmitted directly into a solid stop, it may distort the part. Clamping on draft angles or “mushrooming” the part with excessive force can also cause part distortion. Send us a print of your fixture design; we’ll be pleased to evaluate it and make suggestions. I hold all four corners of my part on solid locators. When unclamped, it seems to “spring” back into a different shape. Why? First, holding all four locating points in exactly the same plane on your fixture is virtually impossible. (See your favorite text on fixture design for an explanation of 3-2-1 principles.) Second, because your part can’t have all four of these points in the same plane, your part is distorting when clamped. Other factors such as stress relief may cause the part to change its “free” shape after machining. My pump turns on and off approximately every 3-5 seconds. Why? There could be several causes. A “spool” valve when used with a demand pump will cause it to turn on and off as its internal leakage bleeds off pressure. Use of spool valves voids warranties on VektorFlo ® pumps. We suggest the use of “zero leak” poppet or shear seal type valves (see Section M). Industrial type double acting cylinders (even high quality ones are not designed for clamping) can have significant leakage across their internal seals. This leakage will not normally be externally visible. Internal leaks from one side of the piston to the other will cause pumps to cycle excessively.
How do I tell if my plumbing is free of obstructions and contaminants? Tubing must always be flushed after cutting. Even if not cut in your shop, it was cut before it came to you. Chips, burrs, dirt and other contaminants have collected inside your tubing and drilled passages. These contaminants can cut device seals, damage valve sealing surfaces, cause erratic operation and reduce service life if not cleaned prior to fixture start up. The use of improper fittings can also cause obstructions and restrictions. Some people have adapted fittings which they had to use in SAE ports. Yes, the threads are the same on SAE and JIC flare fittings. The body length may be different. In one case the use of JIC fittings in an SAE port made a metal-to-metal seal at the bottom of the device inlet port. Obviously the “clamps didn’t work.” Be sure you haven’t created obstructions by using non-standard parts. Is my pump of appropriate size? It is rated for _____gpm, or _____cu. in. per minute. My devices require a total of _____cu. in. of oil to actuate. For most normal size fixtures, a pump rated in gpm (gallons per minute) is not recommended. If your pump is rated much more than 1 gpm, call us; we’d rather give you sound advice now than have you damage your clamps. Be sure that you do not exceed the recommended flow rates for your system. If you aren’t sure, ask us. My pump runs continuously. Is it the right type of pump? Call us. It can often be made to work. Some modifications will probably be necessary. If you have a VektorFlo ® pump which runs continuously, call us immediately (they are not set up to run continuously). I’ve been using a dump pump (builds to pressure, shuts off and releases pressure automatically). Is this pump suitable for hydraulic workholding components? It can be. It will work if the circuitry is properly designed. It may require special circuit modifications or a special pallet decoupler to work properly. I want to make a cut directly against (into) a clamp. Is this possible? Yes, but it will require special design considerations. We encourage that cutter forces always be directed toward a fixed stop. A fixed stop is designed to prevent part movement. A clamp is designed to position and force a part
A-4
NOTE: These cylinders should be avoided in all palletized applications as they may cause pressure loss or backpressure quick disconnects.
© Vektek, July 2024
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www.vektek.com
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