Layout considerations for Valves.
What are the things a piping layout engineer should consider while placing valve in their 3d model? How to locate them? How to access them? How to operate them? can they be easily maintained or repaired? What are the saffety measure one should consider for valves? etc.
In this blog we will specifically talk about the layout related considerations for valves. While
doing layout the designer should consider following four aspects of locating valves.
1. Installation
2. Accessability
3. Operability
4. Maintanability
5. Safety
We will see each of the aspect one by one.
Installation
There are few things that need to be considered regarding how the valves are going to be installed in the field. Flow direction of the fluid is usually marked on the valve body. This need to be checked before installing valve on the line. For some valves such as globe valves and check valves it is important to install valve in in the right flow direction. where as small bore gate valves and butterfly valves does not have such stringent requirements. In case of large bore gate and butterfly valves, they have the flow direction marked on the body.
Accessability
The location where valve has been placed has to be easily accessable by operator. Especially manualy operated valves. The location of the valve should be planned such that the path leads to it does not have any obstructions. Ideally the the valve handwheels and leavers should be loacted at such a height that the human operator can operate it comfortabally in standing postion. If the valves are located at the floor level then extended stems should be provided to ensure that the handwheel reaches to weist level of human operator. The location of the valve in vertical lines are planned such that they come at about torso level of human opertor. This height could be easily somewheer between 1.5 to 2 meters. If for some reason valve has to be located at the height more than the raised human hand reach, then some convenient mechanisms such as chain operators are provided.
Operability
The valves should be easily operated by human operator. The location, height and orientation of the valve hand wheel should be such that it is easy for the human operator to comfortabaly and safely operate it. In case of quarter turn valves such as ball valves, butterfly valves the hand leaver should be placed such that there is no obstruction in the path of leaver movement or the hands that are operating those leavers. Humans can only apply certain amount of force on the valve operators such as handwheels and leavers, according to their physical capacity. This force is somewhere about 25kg. If the valve is large or the valve needs more force to operate than that, the gear operator should be provided. Valve orientation is also important while considering its operability. Some valves have to be located at the height human hands can't easily reach. In such case there orientations are changed and they are oriented downwards or 45 degrees to down direction. But this is not advisable for all valves. The fluid that is flowing inside piping should be suitable to allow such inverted valve orientation. If the fluid has the nature to leake and is hazardous then such inverted orientation is avoided.
Maintanability
Valves have maintananec requirements. After ceitain hours of services or number of operations these valves need to be opened and their trim parts are replaced or repaired. There are few points that need to be taken in to considereation withing layout to ensure that the valves are easily maintainable. Valves that connected with pipe via flange are easy to remove and repair or replace. Valve that have been welded with pipe are not possible to remove without cutting pipes. Such Valves have bolted or removable bonnets. To maintain the valvew these bonets are opened and the valve trim parts are pulled from the valve body for their repair or replacement. To carryout all these activity layout engineer must ensure enough space around the valve. For small size valves the issues are not much for maintananec, but for large bore valves some other consideration also need to be taken in to account. For example, some large valve have internal parts so large that you need some lifting equipment to move these parts or the entire valves to maintanence bay. Engineer must ensure that there is enough space for the mobile crane to approach the valve.
Safety
To avoide safety issues some safety features are provided on the valves itself by the valve manufacturers and some other safety measures have to be made by the layout engineers around the valves. Unintentional operation. There are some scenarios in the plant that the valve get operated unintentionally. For example, plants located in some tropical jungle area it is impossible to prevent some wild life to enter the plant. Some of the animals such as monkeys, koala bears, sloths will enter the plant and these primates have the capability to turn the hand wheels of the valves. They may not have any sinister motive behind it but the valves get operated. There is a famouse video clip that you might have seen in on social media that went viral few years ago in which a sloth is seen to be hanging on the large handwheel of a valve and turning it. What would happen if that valve is controling some hazzardous fluid? hence it is very necessary to ensure proper locking feature in the valves where such un intensional operations could not happen.