MAV or TT Valves. Which is Better?

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When it comes to duplex systems, there are some who swear that a Motorised Alternating Valve (MAV) is better than a TT valve setup. Then you’ve got the other half of the water treatment industry who think the exact opposite. A few months back, we touched upon this topic in a Newsday Tuesday post, where the MD of the company briefly argued with himself about it.

So, which is better? And are there really any differences?


MAV ValveA Motorised Alternating Valve is a way of controlling the water flow to two tanks in a duplex water treatment system. Two Clack CI Valves are used, which communicate with each other via the MAV and an interconnect cable. The process involves putting one tank into “standby” where it can also be regenerated, whilst the other tank is operational. Then, when required, the water flow is switched.

MAV setups enable a continuous supply of water with no downtime. Whilst one tank is operational, the other is being regenerated and is ready to go. The operational tank can continually switch back and forth, giving an uninterrupted flow of treated water.

A secondary but useful benefit for the MAV is its versatility when used as a method of introducing a clean-water back wash. Port A is used for untreated water, Port B used for clean water & Port C connected to the inlet of the valve.

TT Valve

TT ValveThe twin alternating valve is a single valve with its’ own internal MAV/transfer valve mechanism to switch any duplex unit from one tank to the other. It performs largely the same duties as the MAV valve, alternating water flow from one tank to the other, whilst the tank that is in downtime regenerates and goes into standby. Just like the MAV, you get an uninterrupted flow of treated water, all controlled by a single valve.

The TT valve has also proven popular as a replacement for the Fleck 9000 and 9500 twin valve, which have been reported by users as often unreliable and more expensive.

The Differences

Two different setups, to do the same thing. You would be forgiven for assuming that it doesn’t really matter which one you use. Surely the simplest way to make a choice is asking “Which one is cheaper?”

There are differences, though, especially when it comes to the long term operation of a duplex system.




You have a duplex system and for some reason, one of the tanks requires attention. Perhaps after many years of use you need to replace the resin or media within, or for some reason the tank requires attention and maintenance.

If you have a MAV setup: This is no problem at all. you can set a MAV system to operate the functional tank as a simplex (single unit) system. The second tank requiring attention can then be removed from the system for maintenance, replacement and so on.

This is also true when it comes to the valves themselves. If a valve requires cleaning, repairs or replacement, you can simply turn the MAV system into a simplex in the meantime. No downtime whatsoever.

If you have a TT setup: This is a little more tricky and problematic. Due to the fact there is only one valve, you’re going to have to shut down the entire system to perform maintenance to just one of the tanks. This means that for the duration it takes to sort out the issue, the entire system is down. If you don’t have an alternative source of treated water, you’re looking at delays, or having to use untreated water.

Similarly, if something goes wrong with the valve itself, the entire system comes to a halt whilst the necessary maintenance/replacement is carried out.




Is there a difference in quality between MAV and TT? Just how often are you likely to experience problems with either of these setups?

If you have a MAV setup: Evidently, any system is only as reliable as its component parts. When it comes to Clack valves, you’re getting some seriously top quality products. A MAV system setup with Clack parts is not going to cause you issues very often at all.

However, having said that, it is more parts than the TT valve. You’ve got twice as many valves that might go wrong, plus the MAV itself. Three times the amount of things that could potentially have a problem. Admittedly, as we mentioned in the above point, a MAV is very easy to maintain and fix should something go wrong due to the very highly unlikely probability of both tanks having a fault at the same time.

If you have a TT setup: This is still a Clack valve so you’re still looking at a top quality product. Once again, the chances of anything going wrong or requiring attention is very low and any maintenance that does need to be carried out on the valve itself is typically simple enough.

Unlike the MAV valve, there’s only one TT valve in play here. You have just the one piece of kit which can go wrong. With less components you have less chance of something in the system failing or requiring attention. In that regard, it is a little more reliable than a MAV setup. Of course, if something does go wrong, then you’re entire system is down until it can be fixed, which can be a serious hindrance.




You need to install a duplex system into a business to provide treated water. Sometimes, certain components can be much more problematic to install than others. Is a MAV or a TT easier to install?

If you have a MAV setup: There is no getting around the fact that a MAV is a little more complex to install. this comes with the caveat that Clack valves are created with ease of installation in mind. The MAV, plus the two Clack valves all have to be connected correctly, programmed to work in tandem, and all water connection obviously need to be made with care. A mistake during installation could result in a faulty system or incorrectly treated water.

If you have a TT valve: It is a simpler installation than the MAV counterpart. A TT valve only has two ports, the water inlet, and the output port. Connect those two pipes correctly, and you won’t have any problems.




Let’s face it, cost is always a factor. Is there much of a price difference between MAV and TT? If so, which one is more expensive?

If you have a MAV setup: This is more expensive than a TT setup. Simply put, you have to purchase more equipment; there are two valves for a start. Typically, it’s about hundred pounds more expensive than a TT. Is this a significant difference, though? It honestly depends how big the system is. For smaller systems, that’s going to be a fairly big difference. However, once your duplex system is reaching £1,000 and more, the difference of one hundred pounds or so becomes less of a factor.

If you have a TT setup: The opposite of the above. It is cheaper to the tune of approximately £100. For smaller systems, this makes the TT valve a better option, price-wise, but once you get up to larger the systems, the percentage of the overall cost decreases.

In this case, it’s a personal preference and down to your budget. One hundred pounds might be a deal breaker for some, whereas for others, compared to the entire cost of all the components, it’s barely a factor.

Which is better?

This is not one of those guides where we get to the end and says something non-committal like “it depends” or something equally trite. We have an answer.


The MAV setup is superior to the TT valve.


The fact that you can completely shut down one tank, turn the other tank into a simplex system and lose no downtime is a huge merit for the MAV. There is absolutely no downtime when servicing, maintaining and attending to the system. Whereas with the TT valve, no matter how you look at it, you have to shut the system down.

That can be a deal-breaker for companies who absolutely need that water for their business.

This is not to say that the TT valve doesn’t have it’s place. Indeed, when it comes to smaller systems, the TT valve’s value for money becomes more significant. With smaller systems, the downtime can be greatly decreased as it’s simply a smaller unit you have to service, especially if it comes to replacing the tank or media/resin.

Therefore, as with most things in life, it is contextual to the situation you’re in. However, for the most part, the MAV’s sheer versatility outmatches the TT valve and it cannot be stated enough just how important that can be.

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