Ask The Search Engineer 28166

Current induction . . . Metal spheres . . . Force calculation . . .

Dear Search Engineer: I have two hoses that need to connect to each other via quick-disconnect fittings, but the fittings have to stay together if the pressure in the hose gets high. I need some basic theory on designing a pressure-balanced hose connection. —M.S., Newport Beach, CA

Dear M.S.: You could investigate the aircraft sheet metal panels solution: 1/4 turn or 1/3 turn or 1/2 turn screwdriven nuts or "bolts." Alternatively, a slide-snap lock mechanism or steel Velcro. Or you may consider a threadless grooved "bolt" and tepered locking C-ring, such as is or was made by Koh-I-Noor and is still available from its competitors. Dzus 1/4-turn fasteners (http://rbi.ims.ca/4386-516) allow for some misalignment and reportedly work well in vibration-prone applications. McMaster-Carr (www.mcmaster.com) also offers slip-on quick-threading locknuts in stainless steel and zinc-plated, and in standard and metric threads. Another option, Reid Tool Supply (www.reidtool.com), has quick-acting hand knobs, which have a hole drilled at an angle to the threads, allowing the hand knob to be slipped on at an angle, then tilted on axis to engage threads for final tightening.

Dear Search Engineer: Has anyone developed a method to induce a current (power source) from the flow of methane (natural gas) in a pipe? —C.J., BC, Canada

Dear C.J.: It is unclear if you are asking about an induced electric current or not. If not, there are thermoelectric generators used to provide power from natural gas heat sources. These are generally used at remote locations, such as well heads, to power instrumentation where there is no other power source. Check out these sites for more information:

Dear Search Engineer: I need to purchase metal spheres with a diameter range between 1 and 5 inches. They don't need to be precision ground. However, the application requires that a hole be drilled at a 45-degree angle on each side of the sphere. Any idea who supplies such a product? —L.B., DN reader

Dear L.B.: If the quantities support casting, consider that route. The holes can either be cast-in or, if higher accuracy is required, can be drilled using a fixture. The angular relation between the holes is 90 degrees, hence easy to fixture.

Dear Search Engineer: I work in an electronics manufacturing plant where many of the machines have feeder systems (e.g., vibrator bowls where pellets are fed). Where can I find some info about feeder systems, and especially about systems that work with vibration? —M.G., Tamaulipas, Mexico

Dear M.G.: You could learn all the vibratory theory and all the orientation theory from textbooks and still not know enough. I suggest you speak with vibratory feeder salesmen and techies to get a "feel" for the field. Then study the machines you have, and learn their good and bad points. Then, and only then, go for the textbooks, and skim them. After all this, you should be in good shape.

You can also try doing an Internet search for vibratory feeder bowls and feed systems. There are a bunch of them that have websites and standard wares for sale. If you are feeding some materials, you will need to consider the hazards of the unit, though. Most standard units are not equipped for hazardous duty and some modifications will be required for explosive dusts or vapors. Even some plastic dust is explosive in the right concentrations.

Dear Search Engineer: I wish to calculate the force created on a body with a given surface area by virtue of the velocity of fluid flow against the area and the viscosity of the fluid. The body is suspended in the flow with free flow around the body perimeter (i.e., independent of system pressure). Any suggestions?—G.C., DN reader

Dear G.C.: Calculate the kinetic (velocity head) and equate it to the pressure head. Calculate the pressure. Then calculate the frontal area of the immersed body. Then proceed to calculate the impinging force. For a book reference, you may consult the Lyon's Valve Designer's Handbook by Jerry Lyons.

Dear Search Engineer: My company buys steel coils for stamping appliance components. The problem is that we can readily obtain certifications on the steel that have C, Mn, P, S, Al, and Si, but we do not get information on yield or tensile strength unless we pay for it. I was wondering if I have all of the chemical properties listed, is there a program that would either give me an exact yield and tensile strength, or at the very least a range that the material would fall in?—J.H., Mansfield, OH

Dear J.H.: At the time of order, you should be able to request the roll mill's physical and chemical certifications for the material. This information would give the heat number, a ladle analysis, and the physical properties of a sample of the material such as the tensile strength, hardness, and elongation at rupture. Apart from the average values reported, if you need more certainty, you may have to test samples of the material you receive yourself.

Dear Search Engineer: I need to mount some low current electrical connectors (from some temperature sensors) on top of the valve covers of a 16 cylinder diesel engine. Due to the level of vibration and the low current, pin fretting is a concern. I need some sort of isolation system. Temperatures in the area require everything to be rated to 150C or above, eliminating most elastomers, and I haven't been able to find any cable isolators small enough for the approximate 6 oz weight of the sensor connector and bracket. Did I also mention that this needs to be compact, yet tough enough to survive repeated high pressure spray washes?—D.G., Columbus, IN

Dear D.G.: A "U" shaped yoke attached to the valve cover with several small O-rings could hold your connector and provide the isolation required. The O-rings made of these materials can have high temperature contact with diesel fuel, Viton, Kel-F or Nordel, and survive the pressure spray wash. Depending on the length of time the sensors would be attached, these materials can operate at much higher temperatures than the 150C you mentioned. If this is a long-term installation, switch the sensor out for a direct contact thermocouple (such as a type "K") with Teflon jacket or stainless steel over braid with a Teflon core to allow operation to 260C, while the glass braid is workable to 480C. Then extend the wire to a lower vibration, lower temperature area where the bracket could hold the connector (Omega connectors rated to 220C) or at that point a screw-lug terminal block. Standard strain relief grommets can be used to secure the cables up to the connector.