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Ball valves and gate valves both belong to the same family: shut-off valves. When inside a hydraulic system, these mechanical devices interrupt or regulate the flow, depending on whether the valves are fully open or closed, or if they are used in intermediate positions.
It is important to specify that ball valves, given their fast opening and closing mechanism, are not used to regulate the flow but only to stop or interrupt it.
Gate valves, instead, can be partially open during use, even if it should be remembered that in this case the liquid can become disturbed and friction losses can occur.
Gate valves are used to isolate specific areas of the water supply network: during maintenance, in order to do maintenance, with new installations, or for deviating the flow through the conduit. A completely free passage and minimum pressure drop are the strong points of gate valves. If used in an intermediate position, these valves choke the flow in the conduits.
Gate valves get their name from the shape of their closing disc, which can be straight, like a guillotine, or inclined (wedge). The first solution is preferable above all for high delivery capacities, but in both cases it is always the closing disc that determines valve closing or opening according to whether it is raised or lowered. The valve is opened and closed by the rotary movement of a threaded stem connected to the closing disc. To move from closed to open and vice versa, the handwheel needs to be turned a few times. It is therefore a slow operation, which has the advantage of avoiding dangerous hydraulic shocks.
Commonly used in civil and industrial applications, ball valves get their name from their round closing disc; the disc has a bore that is coaxial to the flow. When the valve is open, the hollow ball becomes a part of the conduit and allows the fluid to flow; when it is closed, the flow is completely blocked. To open or close a ball valve, just give it a quarter turn, making the ball rotate along the same axis as the fluid flow, and as such the piping. Even though this quick movement can be made manually (think about taps in a home), it can just as easily be automated, for example using a pneumatic actuator, in the case of industrial systems.
(read also Motorised valves with pre-assembled pneumatica actuator: the advantages of a perfect combination)
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As anticipated, the quick movement can cause hydraulic shock; the wave generated by the movement of the fluid when stopped quickly can damage the piping, a problem that is solvable by installing check valves along the piping.
(read also How to prevent water hammer consequences and avoid damages)
In conclusion, here is an outline of the strong points, and differences between, these two types of valve:
As we mentioned, ball valves operate by rotating a ball 90° while gate valves are controlled by moving a gate up or down. Because of their design, ball valves can perform an almost immediate shutoff, whereas gate valves are not able to act as quickly. This makes ball valves a better choice for applications where fast cycle speed is desired.
The 90° operation of ball valves makes them faster to cycle, both manually and with an actuator. This is a benefit in most instances but can potentially cause water hammer in high-pressure applications. If the pressure is high enough, the pipe could weaken or even break, which is why users of manual ball valves should turn the levers slowly to avoid water hammer.
Gate valves are commonly found in older home plumbing systems.
On/off control for specialized industries including:Ball valves are also found in newer home plumbing systems.
In the gate valve vs. ball valve debate, cost is a major differentiating factor. Up front, gate valves are less expensive than ball valves, but they can be more susceptible to corrosion which means they will need repairs and replacement more frequently. Ball valves have a higher initial cost, but they are the better choice for longevity since they are more durable and highly effective at forming tight seals.
As we just discussed, gate valves are, in general, less durable than ball valves. In moderate or high cycle applications, gate valves will require routine maintenance or replacement. Most ball valves are designed to be maintenance-free and should be replaced rather than repaired. Three-piece ball valves, however, are designed so that the valve seats and seals can be easily replaced without removing the valve from service. This is why 3-piece ball valves are often used in high cycle or high pressure applications where valve seal failure is likely to occur more quickly. However, 3-piece ball valves typically come with a higher up-front cost than the more popular 1-piece or 2-piece body constructions.
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