3-Way Ball Valve Article

3-Way Ball Valves

What Types of 3-Way Ball Valves Are There?

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.

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How a 3-Way Ball Valve Works

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.

L-Port Valve

T-Port Valve

Which Type of 3-Way Ball Valve Is Best?

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.

How Can I Use a T-Port 3-Way Valve but Still Shut off All the Flows?

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.

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How to Tell Direction of Flow in a 3-Way Ball Valve

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.

Why Won't My Flows Mix Properly with a 3-Way 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.

Do I Need Unions or Flanges on a 3-Way Valve?

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.

5 Things You Should Know When Choosing a 3-Way Ball Valve

• L-Port valves can only direct the flow through 90 degrees or fully shut it off
• T-Port valves can direct the flow in any way you want, but can't completely shut it off
• A valve with unions or flanges on each of the ports makes servicing much easier
• The arrow diagram on the top of the handle represents the position of the cut-out ball inside the valve
• To mix flows using a T-Port valve, the dynamic head of the two mixing streams should be consistent

OK, if there is no process reason, why would you pick a reduced port valve over a full port? Historically, the reason has been cost. For some reason, prior to about there was a significant cost savings for reduced-port valves. That stared to change around , and by you had to look very closely at your cost estimates--in some sizes the reduced port valve was actually more expensive than the full port valves. It is still true today. Even when the reduced port valves are cheaper it is usually a pretty small difference. On the other hand, it can be really hard to get a pig to scamper through a reduced port valve, and you cannot run a smart pig through a reduced port valve.

If you can say that the cost is a wash, then I can not see any reason why you would ever buy a reduced port ball valve.

Now if you were asking about selection criteria between a full port "floating ball valve" and a full port "trunnion ball valve" the discussion gets more interesting, but you didn't ask that.



David Simpson, PE
MuleShoe Engineering


"Life is nature's way of preserving meat" The Master on Dr. Who

There really is not a process reason to select a reduced-port ball valve over a full-port ball valve. There is a measurable dP across a reduced port valve, but work done at Southwest Research (for gas measurement, but the concept carries over) showed that with the beta ratio of a reduced port valve virtually none of the (small) dP is "permanent". That means that if you measure the pressure 10 diameters upstream and 10 diameters downstream of a reduced port ball valve in the same flow you will get essentially the same dP (down to a fraction of a mm of water column) as a full port valve.OK, if there is no process reason, why would you pick a reduced port valve over a full port? Historically, the reason has been cost. For some reason, prior to about there was a significant cost savings for reduced-port valves. That stared to change around , and by you had to look very closely at your cost estimates--in some sizes the reduced port valve was actually more expensive than the full port valves. It is still true today. Even when the reduced port valves are cheaper it is usually a pretty small difference. On the other hand, it can be really hard to get a pig to scamper through a reduced port valve, and you cannot run a smart pig through a reduced port valve.If you can say that the cost is a wash, then I can not see any reason why you would ever buy a reduced port ball valve.Now if you were asking about selection criteria between a full port "floating ball valve" and a full port "trunnion ball valve" the discussion gets more interesting, but you didn't ask that.David Simpson, PEMuleShoe EngineeringPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora."Life is nature's way of preserving meat" The Master on Dr. Who

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