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  1. #1
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    Dec 2016
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    Valves and fittings

    How to simulate valves and fittings?

    I was planning to use a coefficient. Is there a guide for coefficients for different fittings (valves, elbows, tees)?
    I was also planning to use equivalent length (EL) and to add the additional length. However, I got a doubt. The equivalent length for valves have a wide range. Globe valve EL is much higher than EL of gate valve. Why is that? What is the difference between the valves?

  2. #2
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    Vladimir,

    It is really up to you if you add length (or minor losses) to account for fittings. However, because most users are using nominal pipe diameter and a reasonably conservative C-factor, I have found in hundreds of calibrations that most system fittings minor loss impacts to be fairly negligible or at least reasonably accounted for by using the nominal pipe diameter and a reasonably conservative pipe C-factor. But if you wish to add minor losses for these on the pipelines are account for them with an "equivalent length" you certainly can do this, its just that most modelers often do not. There can be certain circumstances like at a pump station where you may have limited head on the suction side or need to account for the minor losses because they may become non-negligible where accounting for the losses is important, but for most of the water system you generally may find your equivalent length added is essentially minimal such that the additional headloss added is so minor that it can be ignored. Do a few calculations for yourself to see.

    Recall Minor loss headloss is HL_ml = K *(V^2/(2G)) where K is the minor loss Coef and G is the Gravity constant and V is the velocity.

    For US units G = 32.2 ft^2/s^2 such that the V^2/2G term is only ever greater than 1 when the pipe velocity is at 8 ft/s or higher which is a very high velocity.

    Except for fireflow most systems pipe velocities are generally low under normal operation (most under 3 ft/s or less for non-fireflow conditions) that the velocities are so small that minor losses are negligible because the hydraulic grade line is normally fairly flat across a pressure zone. But for long transmission lines or other places where the velocities could be higher minor losses could become more significant, but for most cases, they really end up being "minor" and don't contribute much to the overall headloss except in certain situations like at control valves.

    Some links form a quick google search:
    Minor Loss table: https://www.engineeringtoolbox.com/m...pes-d_626.html
    Equivalent length calculation: https://www.engineeringtoolbox.com/e...hod-d_804.html


    The difference between a gate valve and a globe vale is quite dramatic. a globe valve is often used as a control valve and has a very turbulent path to get through it, where as a normal gate valve would when fully open have little impact on the flow. This is why a globe valve has a K of 10, and Angle valve (also used for control vlaves) has a K of 2 while a fully open gate valve has a K of only 0.15. This is a huge difference and is why these would have significant differences in equivalent length as the K for a globe valve is roughly 70 times larger that of a fully open gate valve (10/0.15 = 66.7). Gate valves and butterfly valves are the typical normally open isolation valves used in most water systems. Gate valves are usually for smaller pipeline locations and butterfly vlaves for larger pielines because gate valves as they get larger require more space to install than butterfly valves. For this application these valves should ideally not cause significant headloss when fully open which is thier normal operating position. These type of valves are typically open or closed and are not used for "throttling" because they would wear out prematurely.

    Nice comparison here of Globe vs gate valves: http://www.teervalve.com/12-main-dif...d-globe-valve/


    Globe valves are typically used in control valve operations like Pressure reducing, Flow control, or pressure sustaining applications. ClaVal is a major control valve provider in the US and essentially all of their control valves (Pressure reducing, flow control, pressure sustaining, etc) use the same globe or angle valve and just adjust the piping to adjust the valve opening and closing based on the valve type. Here is the main valve they typically use. Most water systems seem to prefer the globle style over the angle style because is can be placed in line with the pipeline direction without adding fittings you would need to connect an angle valve. Link to thy ClaVal Hydrotol 100-01 valve: https://www.cla-val.com/documents/pdf/E-100-01.pdf. Most of these valves used to control flow will have a large headloss associated with them. Normally this is ok, because the valve itself is inducing headloss to control the flow through the valve, but this is why multiple valves are needed to handle large ranges of flows as a single valve usually cannot handle a large flow range. Typically most valves have a 1-10 flow range such that if the low flow is 3 gpm the high flow would be near 30 gpm or if the low flow is 30 gpm then the high flow would be around 300 gpm. Depending on the flow range needed this is why you see most PRV vaults usually having 2 or 3 valves to handle the range of flows needed.

    Quote Originally Posted by Vladyman View Post
    How to simulate valves and fittings?

    I was planning to use a coefficient. Is there a guide for coefficients for different fittings (valves, elbows, tees)?
    I was also planning to use equivalent length (EL) and to add the additional length. However, I got a doubt. The equivalent length for valves have a wide range. Globe valve EL is much higher than EL of gate valve. Why is that? What is the difference between the valves?

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