7 MPa Planning
Frequently Asked Questions
Is my plumbing 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. Be sure you haven’t created obstructions by using non-standard parts. Is my pump of appropriate size? It is rated for____l/min, or _____cm 3 per minute. My devices require a total of _____cc. of oil to actuate. For most normal size fixtures, a pump rated over 8 l/min. (liters per minute) is not recommended. If your pump is rated much more than 4 l/min, call us, we’d rather give you sound advice now than have you damage clamps and have to sell you replacements. Be sure 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. I’ve been using a dump pump (builds to pressure, shuts off and releases pressure automatically). Is this pump suitable for workholding? It can be. It will work if the circuitry is properly designed. It may require special circuit modifications to work properly. I want several sequenced operations to happen on my fixture. Can I put three or four sequence valves in series? We do not recommend it. Our sequence valves operate better if run directly from the main hydraulic supply line and set at different pressures. We recommend at least 1 MPa differential.
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. 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 fixture building 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. I want to limit the pressure into a sequenced hydraulic circuit. Which valve would I install first? We recommend you avoid putting one special function valve behind another if possible. If you must, put the pressure limiting valve after the sequence valve. This avoids the limiting valve being shut off before the sequenced circuit is fully actuated. I want to make a cut directly against (into) a clamp. Is this possible? Yes, it is, 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 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.
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 identify some common problems you might encounter. What is the advantage of 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 when “return” time is critical (as in some CNC systems). What should I watch for when selecting fittings, tubing and hoses ? Some fittings and hoses which are locally available (not from Vektek) have extremely small orifices which restrict flow. The use of G 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 back pressure of returning oil. Proper sizing of fittings for main feed lines and device supply lines will normally be accomplished by using an appropriate fluid distribution manifold. Device fittings are G 1/4 or G 1/8. Main feed lines should be at least 8 mm to avoid restrictions.
© Vektek January 2019
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