Copyright Goodheart-Willcox Co., Inc. Chapter 8 Fluid Storage and Distribution 197 where: V = Flow velocity Q = Flow rate A = Conductor cross-sectional area Care needs to be taken to use quantities with the same units. This formula, for example, can use a fl ow rate of gallons per minute (gpm), but it may be useful to convert to inches per second (in3/sec) if the conduc- tor is also measured in inches. Cubic inches per second can be easily calculated by using the formula: in3/sec = gpm × 231 in3 60 sec Fluid Velocity in a Conductor Calculate the velocity of the fluid in a conductor with a 1/2″ inside diameter that is moving five gallons per minute. 1. Calculate the inside cross-sectional area of the conductor: Area = πr2 = 3.1416 × .25″ × .25″ = 0.196 in2 2. Calculate the flow rate in cubic inches per second (in3/sec): in3/sec = 5 gpm × 231 in3 60 seconds = 19.25 in3/sec 3. Calculate the average fluid velocity in the conductor: Velocity = 19.25 in3/sec 0.196 in2 seconds = 98.21 in/sec or = 8.19 ft/sec EXAMPLE 8-1 8.3.3 Temperature Although pipe and tubing are generally not affected by temperature, both ambient and system operat- ing temperatures must be carefully considered when selecting hose, Figure 8-26. Very high or very low tem- peratures can adversely affect a hose. Extreme ambient temperatures can reduce hose service life by causing deterioration of the hose cover and reinforcement materials. Continuous system operating temperatures that are at or exceed the rated temperature of a hose will cause deterioration of both the hose inner tube and cover. This also results in a shortened service life. materials distributed by the conductor manufacturer. These published ratings show the recommended oper- ating pressure limits for conductors used in a continu- ously operating system. These recommended maxi- mum pressures are typically no more than 25% of the burst pressure rating of the conductor. Care should be taken to avoid selecting a conductor with a recom- mended maximum operating pressure that is below anticipated system pressures. Although every attempt should be made to elimi- nate operating situations that produce pressure surges, they need to be considered a possibility. Therefore, shock pressures also need to be considered when selecting a conductor for a system. If system pressure surges are frequent, the service life of system com- ponents will be considerably shortened. Conductor- related problems caused by pressure surges can be reduced by selecting a conductor that has a higher rec- ommended maximum pressure rating than the normal working pressures in the system. 8.3.2 Flow Characteristics A conductor must be large enough to accommodate the fl uid fl ow required to operate the system. The inside diameter of the conductor establishes fl ow capacity. Flow capacity is also directly related to fl uid velocity. The higher the fl uid velocity, the higher the fl uid fl ow rate for a given conductor. However, if the fl uid veloc- ity becomes too high, it can produce system operating problems. Different fl uid velocities are recommended for different types of system lines and conductors. For example, the average fl uid velocity in a pump inlet line should not exceed four feet per second (4 ft/sec). Aver- age velocity in working lines should be held below 20 feet per second (20 ft/sec). The velocity of the inlet line fl uid is restricted to prevent the formation of a vacuum that is too far below normal atmospheric pressure. Excessively low pressure in an inlet line can result in pump cavitation. Cavitation can cause major pump damage. This prob- lem does not relate to working lines, as they normally operate above atmospheric pressure. A typical work- ing line pressure range is from slightly above atmo- spheric pressure to the maximum relief valve settings. The problem with the movement of fl uid through working lines is not pressure, but turbulence. Exces- sive fl uid velocity produces turbulent fl ow, which causes resistance to fl uid fl ow. This results in pressure losses in the system, which are converted into heat. The heat, in turn, results in increased system operating temperatures. The average fl uid velocity in lines can be calculated using the formula: V = Q A