There are two types of 3-way ball valves: L-Port and T-Port. An L-Port can send flow one way or the other or can shut it off completely. A T-Port will perform all the same flow tasks as an L-Port but cannot be shut off. In addition, the T-Port can mix flows by sending or receiving flow to/from both ways of the Tee. The "T" and "L" refer to the shape of the opening in the ball.
A 3-way ball valve works by turning the handle, which rotates a ball in the valve body, to align the cut-out channels in the ball with the inlets and outlets of the valve. The "L" shape cut-out of the ball on an L-port valve sends fluid through 90 degrees from one port to another. The "T" shape cut-out of the ball on a T-port valve can also send from one port to another, but can also be rotated so that the T aligns with the "T" shape of the valve and all three ports are mixed.
The best type of 3-way ball valve for your application depends on whether you foresee a need to shut off all ports at any stage of operation or mix all three flows. If there is a requirement to close the valve completely, then you should choose an L-port. If there is a requirement to mix all three flows, then you should choose a T-port.
To shut off all the flows on a T-port 3-way valve, a separate valve must be added to the two opposite branches of the tee. To close the flow off, the two valves must be closed and the ball in the 3-way valve turned to face the rear of the valve. A better solution is to install a tee piece with a single valve on each branch.
On a 3-way ball valve there will be a tee-shaped arrow indicator on the handle which mimics the cut out section of the ball inside the valve. By referring to this mark, it can be ascertained which direction(s) the flow will travel through the valve.
To mix flows accurately on a 3-way T-port valve, it is important that both the feed pipes have the same, consistent, static pressure head and that the pipework is of a large enough diameter so that when changes are made in the flow rates, the static head does not change significantly. Mixed flows from constant height header tanks are easier to balance, whereas those from pumped supplies are not (unless the pumps are fitted with constant pressure inverters). If this is not the case, then the pressures in the pipe will change over time and the mixing ratios will also change over time. This change can sometimes take hours or days to be large enough to be noticed.
At some stage a valve is likely to either become blocked or wear out. Unions or bolted flanges on the valve allows the valve body to be removed for servicing or replacement. Without the ability to do this, the pipe will need to be cut on at least two of the three sides of the valve, which will result in a much longer downtime for your plastic pipe system.
Our 3-way ball valves come with unions as standard.