Altitude valve 1

[WaterGIS]

Hi All..
we are about to install altitude valve between 2 water tanks the 1st tank is 250 m (elev) and the other one is 90m elev. the valve will be for the lower one , the distance between them is about 2km and the diameter (600mm). The aim of installing this valve is to control the elevation of the tank, to work as pressure reducer and to prevent water hummer. Well it does this proposed work??

Regards,

 

[yogibear1]

The altitude valve installed in line to the lower tank will provide head loss (as you intend) and should cause a proportional amount of water to divert to the other tank. Is it your intent to have equal filling rates to both tanks?? You will have to calculate the proposed loss desired and crank that into the pilot circuitry of the altitude valve. Be sure to have a level sensing device in each tank to provide feed back, and a to shut off the delivery system (pumps or shut off valves) when the tank(s) reach max level. The tanks should be vented as well as have overflows.
The valve if properly set-up can be used to control the water elevation in the lower tank (it can act as a shut off). It will reduce pressue in the line to the lower tank. I don't see it acting as a water hammer prevention device, except in the speed with which it closes (controlled via needle valves in the pilot lines).

 

[Bbird]

If I guess your intention correctly the altitude valve is intended to give you a better control on the flow to both tanks. Under normal circumstance the lower tank will get filled first before the higher tank as water always takes the line of the least resistance.

The altitude idea sounds Ok but in practice there may be instability problem with the control mechanism necessitating an expensive valve manufactured for control purposes.

Your system characteristic of the pipeline to the lower tank will be relatively flat and with a small static lift (90m at flow=0, assuming the source of water from elevation 0) but the leg to the higher tank has both higher static lift (250m) and a steep gradient on account of the extra 2km skin friction. When plotting the two together on the same discharge/head graph the vertical difference between the two is the head loss you need to replicate in the altitude valve to produce equal flow in the system. It should be obvious that the head loss needed to balance the flows will increase with the discharge rate and continuous flow measurements will have to be installed in at least one half of the system to acquire data for continuously updating the setting of the altitude valve.

If one can control the flow in 50%:50% split one should be able to do it any other combination.

We can leave out the effect of the change of the static lift by the water level moving up the tank as this local effect can be overcome by taking readings on the water level of both tanks to update the two pipeline characteristics dynamically. Thus theoretically the altitude valve can work satisfactorily.

The water hammer effect is unlikely to be a problem as the altitude valve by its very nature will be slow acting and the valve is controlled as described above. I could foresee problem only if the control system malfunctions when the valve is allowed to close quicker than the designed rate but this can be mitigated by installing fail save dampers. Each pipeline has a pressure rating from which the maximum flow change (or the valve closure time) must be observed to avoid damage to the line.

 

[PUMPDESIGNER]

Altitude valve will control filling of the 90M tank as you would expect, and thereby produce some effect on the 250M tank, but cannot be predicted based only on the information you provide.

If you have centrol control system on this then you may want to put in a different type of valve you can control as altitude valve with addition of being able to control the position of the valve, full open, full closed, or modulate. That would allow you to get more function. Possibilities are motor operated gate, diaphragm valve with modulating ability.

PUMPDESIGNER

 

[hydrae]

I assume you are currently fill the upper tank with your source and it is currently operating normally, you have a new tank? at the lower area and you want to fill it using the upper tank as its source but not fill it so fast that you lower the pressure in your upper service area.
as such I would recomend an altitude valve with pressure sustaining control loop (also known as a backpressure valve). The altitude portion of the valve allows it to open if the lower tank is needing water, while the pressure sustaining portion will only allow filling if there is extra water available from the upper tank and the demand in the upper zone is not taking everthing.
There are several manufactorers of pilot controlled diaphram operated control globe valves, use one with a long standing service rep in your area with a good supply of spare parts. You do not want to wait a week to get a replacement gasket for your valve five years from now.

Hydrae

 

[WaterGIS]

Hi all thanks for your replies it is highly appreciated, the lower tank will take water from the higher one. And the aim of the valve installation is to control the level of the water automatically by the valve, but we were afraid that a water hammer will be generated. Will this be safe and correct? Regards,

 

[semo]

The altitude valve will work in the situation you describe. I have used one in this scenerio before. Hydrae is correct with the pressure sustaining control loop. Where you place the valve can have some impact on its operation. The closer to the tank you can place it the better. The valve will have pressure sensing lines before and after it. If the valve is close to the tank, the post pressure sensing line should be tapped to the tank. It will operate better than tapping the line immediately after the valve. There will be less effect on the pressure during the valves opening and closing. These valves have adjustable closing speed controls to eliminate the water hammer effect.

If the funds are available, I would rather use an electrically/hydraulically operated butterfly valve with controls (ie. smart valve) that will allow the opening and closing based on a storage tank level sensor. You will get longer service life with less maintenance.

 

[PUMPDESIGNER]

semo is very correct. Direct control is better because you can determine how the valve acts and if pressure surge becomes a problem then you can change its behavior.

Pressure surge is hard to predict because a simple altitude control valve will bahave based on the pressure differential across the valve which changes constantly, and also based on how you equip it, adjust it, etc.

Direct control as semo suggested (and I suggested also in my first post) allows you full flexibility to modulate the valve without modifying the valve.

A highly experienced valve builder could pick the required valve features and install it and set it up. But where is that guy? Direct control allows you to learn as you go how the system is operating and then make appropriate adjustments.

PUMPDESIGNER

 

[semo]

I'm back at work and looked up some info on the valve that I used in my situation. The reason I used this valve is that I had a high and low water system (two towns) approximately 3 miles apart that were connected by one 4-inch water main. The low system had the tank in the central part and was not directly connected to the supply main. Instead the main connected to the low system at the edge of town. Additionally, funds were limited so that a smart valve could not be used.

A valve as discussed above was used. The altitude controls were used so that the tank could have some turnover in it and was fluctuated approximately 5 feet.

You will want to contact a control valve manufacturer with your specifics so that they can design the valve at your pressures and flows. I utilized a Watts valve in my application. I have a contact name and number that has worked on these situations before if you wish to e-mail me.

Also be sure to keep the valve location dry and easily accessible. Especially if it is underground. These valves do typically have a lot of maintenance; which can be reduced by their location.

 

[stanier]

The use of a butterfly valve could well increase the likelihood of waterhammer. they are not very good for control purposes except in a narrow band of operations. In any event the system should be modelled to establish what will happen.

A vee ball or eccentric plug would give better control characteristics. I have use altitude valves in such circumstances. The problem with speed control is that it is generally by pilot valve mounted on the valve itself. people tend to fiddle with the settings so a cage over the valve is necessary.

No one procrastinated their way to the top

 

[semo]

I agree stanier, a plug valve is probably the best solution for throttling the flow as it has a larger control range. A butterfly valve gives little throttling capabilities until the last 15%-20% of its operating range. However for an open/close situation as is being used, the valve operator can be adjusted for a slow close that will reduce or eliminate the water hammer. There is a large cost difference between these two valves also.

The entire situation must be fully examined in relation to the water hammer however. Just because something works in one situation doesn't mean it works everywhere. I have used pumps with solid state drives that have no hammer effect when the ramp up/down time is extended; however, I have also used the same pumps where water hammer occurred regardless of the ramp times. These situations required VFD's or pump control valves.

Yes, the altitude valve speed control is adjustable by a pilot valve that can be fiddled with. This may occur more often in a manufacturing facility than in a rural setting; but, the operator should become familiar with how the valve operates so that he can accurately adjust the pilot controls. Tinkering with these valves can lead to operational problems. The location can have a lot to due with the valve protection. These types of valves where I work are typically used in remote locations where the operator seems to be lucky if he checks on them once a year and that is why I mentioned that the conditions at the valve location can affect the O&M.

 

[hydrae]

I have some comments here:

The example has a lot of head to break, most AWWA butterfly valves will lose their resilant seat breaking that kind of head over a short period of time, I have seen a 14" (350mm) lose it's seat in six months breaking only 60 m of head, it was used to fill a reservoir as a throttling valve.
On the recomendations of using plug or butterfly valves how is the cavitation damage prevented? These are full port valves with resilant seats, and when the seats do wear out how are they repaired? replace the entire moving mechanism, the whole valve, or glue on new material? how do you get to the operating mechanism?

Pilot operated control globe valve manufacturers (cla, watts, ames, OCV, bermand) will list a maximum pressure drop per outlet pressure so cavitation can be avoided. In your (waterGIS) case you may want to use two globe valves in series to break the pressure without going into a cavitation zone, each valve would have a backpressure setting and the second valve have altitude overide.
Some of the manufacterers may instead install cavitation reduction devices inside the valves to reduce or prevent caviation. They also provide low cost rebuilding parts that are easier to install than replacing the entire valve, in most cases you just replace the diaphram and the sealing seat which is bolted on with a ring not glued in place. The design of the sealing seat is such that it is not used to break the pressure when operating above a minimum flow.
In all cases may want to reduce the size of the control valve to a smaller size that the 600mm size of pipe, this will make the valve operate in it's prime control range.

Hydrae

 

[stanier]

If extreme pressures are to be let down then tortous path valves such as manufactured by CCI should be considered.

No one procrastinated their way to the top

 

[PUMPDESIGNER]

stanier - That was a good link, neat stuff.


PUMPDESIGNER

 

[semo]

You're right hydrae, I would not want to install any type of control valve in-line without shutoff valves surrounding it so that repairs or replacement could be performed.

I have not had a lot of experience with metal seated valves; but, they might be used for the high pressures;

I also agree that I would probably install another globe valve as a pressure reducing valve and flow control at some point in the line to keep the line pressures down and the flow rate reduced. On a lot of systems there would be users on the connecting line and a reduced pressure would be needed (at least at each service connection).

The control valves do not have to be placed at the low tank, they could be placed nearer the upper system to keep the pressures on them low and reduce the damage. The controls could utilize telemetry for the 2 km distance. Flow restriction can also be used to keep the rate and cavitation down by placing the control valve in a smaller bypass line. I'm throwing out ideas; but, the actual hydraulics and configuration for the particular system will dictate what can and can't work and where things might be placed.

 

[WaterGIS]

Hi Semo, I would highly appreciated if you send me the contact name and the email of the person that he has worked in similar situation,
Hi PUMPDESGNER , what other information you need so that you could predict the effect on the 250M tank,
So if any one needs any information about this case so that he could propose any solution please contact me,
Regards,

 

[semo]

You can contact Elmer McKinley with Watts Control Valves. Watts will model the system based upon your info and select the valve options you will need. I always look over what they propose however, to ensure I feel confortable with their recommendations. His # is 713-320-3962. You can tell him Richard Cochran gave you his number.

 

[PUMPDESIGNER]

I would have to see the whole system on paper with all available data. Even then I might require onsite studies of some things such as flow charts and pressure charts over 1-2 weeks. Not interested though, I have a full basket now.

PUMPDESIGNER