Buckling

The analysis and design of compression members can differ significantly from that of members loaded in tension or in torsion. If you were to take a long rod or pole, such as a meterstick, and apply gradually increasing compressive forces at each end, very small axial deflections would happen at first, but then the stick would bend (buckle), and very quickly bend so much as to possibly fracture. It is advisable to distinguish compression members according to their length and according to whether the loading is central or eccentric.

Contact stress (sphere)

The most general example of contact stress occurs when each of the contacting bodies has two different radii of curvature-the radius in the rolling plane is different from the radius in the plane perpendicular thereto, both planes passing through the axes of thrust forces.

Contact stress (cylinder)

When two bodies with curved surfaces are pressed together, the line of contact changes to the contact surface and the stresses in the bodies become spatial. Contact stress problems occur at the point of contact of the wheel with the rail, in the valve manifolds of internal combustion engines between cams and valve tappets, in gear engagement and in rolling bearings. Characteristic disturbances that can be observed are cracks, wells or peeling of the surface layer of the material.

Allowable Hertz pressure

It is the pressure that arises at the point of mutual force interaction of two bodies with defined surface curvature.

The bolt connects 2 flanges (torque load)

Serious bolt failures often occur in the operation of machines and machinery. In some cases, this phenomenon occurs even when the designer is convinced of sufficient safety of the bolted connection (given the external load conditions). The failure is most often caused by the underestimation of the limit state of the bolt connection or by the lack of reliable data for a thorough analysis of the strength conditions of the connection. These are especially experimentally obtained data, which are necessary both for the theoretical calculation and for the determination of the optimal design of the bolt connection.

The cross pin connects 2 flanges (torque load)

In the marked diameter d1 and there must be no other weakening element in the cross-section in which the pin is located.

Square head for shaft-hub connection

The advantage of this connection is easy assembly and disassembly. The disadvantage is the low manufacturing precision and consequent consequences for limited speeds and small torques.

Hydrodynamic calculation Needle valve - closing flow against the direction of movement of the piston

When designing a Needle valve, it is necessary to recognize several important parameters that express the hydraulic conditions and dynamic effects of flow in the valve. The basic parameters are the cavitation coefficient, the pressure loss, the flow rate and the resulting hydrodynamic forces acting on the movable part of the valve. You need to know the values of these parameters depending on the opening of the valve.

Hydrodynamic calculation Needle valve

When designing a Needle valve, it is necessary to recognize several important parameters that express the hydraulic conditions and dynamic effects of flow in the valve. The basic parameters are the cavitation coefficient, the aeration coefficient, the pressure loss, the flow rate and the resulting hydrodynamic forces acting on the movable part of the valve. You need to know the values of these parameters depending on the opening of the valve.

Hydrodynamic calculation Howell-Bunger valve

The Howell Bunger valve today is one of the most widely used valves of dam outlets. Its construction is simple and the operating forces during opening are relatively small. Other advantages compared to other types of valves include efficient effluent damping as well as good aeration of water, which can often be critical to improving its quality.

Articulated trunnion in the rod

The trunnion is used to pivot the machine parts that transmit forces perpendicular to the trunnion axis. The trunnions can also be used for short axes such as wheels, pulleys, etc. They are usually mounted with clearance, allowing relative movement. The connecting Trunnions must be secured against axial displacement.

Key(s) for shaft-hub connection

If the shaft is loaded with the bending moment in the joint, the bending stress must be checked. If the shaft is loaded with a shear force in the joint, the shear stress must be checked. The shaft may be load in the joint by axial force. The shaft must be checked for axial stresses. When calculating the different load types, it is necessary to calculate the combined stress.

Hydrodynamic calculation Butterfly valve (lenticular disc)

Today it is required from the butterfly valve to be able to safely close the piping at maximum flow. We need to know not only the mean values of the hydrodynamic forces and torque values, but also the pulsation, the maximum amplitude, when designing the butterfly valve and the connecting pipe. We also need to fully understand the effect of cavitation, the effect of aeration and the effect of the different placement of the valve in the pipeline on its hydraulic and dynamic characteristics.

Hydrodynamic calculation Spherical valve

Today it is required from the spherical valve to be able to safely close the piping at maximum flow. When closing from an open position, the body resists the current flowing through not only the internal rotating body but also through the obstruction of the outside. The flow is very complex in this case and in certain opening positions the valve is extensively stressed by hydrodynamic forces.

Maximum allowable pressure PS of a valves

Maximum allowable pressure PS must be based on the most stringent conditions, which act on the valve. According to the maximum allowable pressure, the PN valve must be selected.

Cavitation for Outlet piping and valves

In practice, however, zero pressure in the pipeline cannot arise because water is excreted out of the water when the pressure drops, the gases contained in the water and forming water vapor. At normal temperatures, the water vapor pressure is about 0.1 m of the water column and therefore the cavitation boundary will be 10 m under the pressure. So, we will expect cavitation phenomena wherever we experience under-pressure, that is, pressures lower than atmospheric, and where the under-pressure reaches considerable values approximating the absolute value of barometric pressure.

Hydrotechnical calculation for Outlet piping

It is used to drain excess water from the dam, if necessary, to empty the dam. Each outlet has at least two valves: operational and revision. To achieve complete safety, an emergency valve is placed, which is permanently in the open position and is designed to quickly close the piping in the most critical cases.

Radial pin for shaft-hub connection

The easiest and oldest way joints. It is a joint with a shape contact. The pin serves primarily to ensure the mutual positioning of the two parts. They are cylindrical or conical. The pins are dimensioned under simplified assumptions without will and without the pressing effect. When designing a pin, the cross section of the pin in the shear area must be the nominal cross-section of the pin.

Longitudinal pin for shaft-hub connection

The easiest and oldest way joints. It is a joint with a shape contact. The pin serves primarily to ensure the mutual positioning of the two parts. They are cylindrical or conical. The pins are dimensioned under simplified assumptions without will and without the pressing effect. When calculating the pin, the length of the pin should not be considered, which is different from the nominal cross-section see, for example, the thread in the pin etc.

Allowable stress

Reliable use of the products depends on how the designer ensures that the maximum stress in their critical locations is less than its limit value. This inequality must be met with sufficient margin to cover all sources of uncertainty of the relevant quantities; Under these circumstances, violation may occur only in exceptional circumstances.

Steel piping on saddle supports

The pipe line is firmly anchored at both ends - one ends is anchored in the foundations of the intake and the other in the foundations of the power house. Apart from these, anchorages are installed at bends and also near the expansion joints of long straight sections. Axial forces acting upon pipes are taken up by the anchors. The pipe is axially fixed to the blocks. Since the piping in these blocks is axially trapped, a dilatation piece must always be inserted between the two blocks to allow dilatation of the pipe at temperature changes. Between the anchor blocks the pipe is supported by concrete piers which take up reactions acting perpendicularly to the axis of the pipe and they permit shifting in axial direction.

Effective closing time factor

The water hammer formula is valid assuming linear flow characteristics (at even closure - the linear relationship between the flow and the position of the closure valve). This assumption is difficult to accomplish with most valves without pre-treatment (modification of structural characteristics). Only a partial part of the total stroke influences the substantial flow limitation.

Calculation dimensions for drive by parallel or diagonal square head ISO 5211

The advantage of this connection is easy assembly and disassembly. The disadvantage is the low manufacturing precision and consequent consequences for limited speeds and small torques.

Calculation dimensions for drive by key(s) ISO 5211

The feather key are used to transfer the torque between the shaft and the hub. The feather key are inserted into shaft and hub grooves. The torque is transmitted only by the flanks of the feather key.

Bolt stressed by bending

The additional bend in the connecting screws must be avoided as the resulting bending stress can be several times greater than the tensile stresses of prestressing and operating forces.

The stress in pipe when changing temperatures

The piping system can be designed with expansion joints to prevent axial forces from changing the temperature, but the piping system may become uneconomic (expensive). Another disadvantage of the expansion joint is the non-transfer of the axial forces, so that if the expansion joint is inappropriately positioned in the duct system containing a member which forms axial forces (valve, elbow), the expansion joint may be destroyed.

Water hammer

Is a pressure surge or wave caused when a fluid, usually a liquid but sometimes also a gas, in motion is forced to stop or change direction suddenly, a momentum change. A water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.

This pressure wave can cause major problems, from noise and vibration to pipe collapse. It is possible to reduce the effects of the water hammer pulses with accumulators, expansion tanks, surge tanks, blowoff valves, and other features.

Water hammer computation formulas are for linear closure. The procedure below shows how to proceed at nonlinear closure.


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