When to use gate valves and when to use ball valves

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: flow stopping and choking

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.

Ball valves: speed and versatility

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)

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)

Which are better: gate valves or ball valves?

In conclusion, here is an outline of the strong points, and differences between, these two types of valve:

• when fully open, gate valves and ball valves both have scarce pressure loss and, as such, an optimal hydraulic yield;
• ball valves cannot be used to regulate the flow, while gate valves can, even when at the intermediate position;
• ball valves are easy to move: just turn the handwheel 90° to open or close the valve. This fast movement, however, favours hydraulic shock;
• gate valves are slow to open and close, and this is why they tend to avoid overpressure waves;
• to avoid clogging, ball valves should be used with clean water and fluids that do not contain suspended particles;
• gate valves can be used with denser, more dirty liquids, for example wastewater and sludge.