Isolating Valves for Chilled Water Systems 4

[IBechir]

I already posted this in the HVAC/R forum but received no replies so I am re-posting here.

The below inquiry is regarding valves for a commercial building chilled water piping system (i.e. clean water @ 4'C with rust inhibitor chemical).

For large chilled-water pipes, dia 200-350mm, what type of isolating valves would you use?

I am aware of the differences between butterfly and gate valves; namely the price, size and weight, but I am concerned that butterfly valves can be closed too quickly so a water hammer may have a higher chance of occurring (I read that for large valves the last 20% of the quarter turn controls 80% of the flow).

Also, I am aware that gate valves can be repaired without removing it from the pipeline but I am not sure if this means that some repairs can be done without draining the system. If the system still has to be drained, what advantage is there for being able to repair a gate valve with disconnecting from the pipe?

Thanks in advance to all that share information.

 

[DRWeig]

I've never seen anything but a butterfly valve for chiller isolation...

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[LittleInch]

If you're concerned about closure speed, specify a gear operated closure with a set number of turns required to go from open to close. That should be sufficient to slow the flow down over a reasonable period of time. The quarter turn handle levers on smaller valves can be very quick indeed.

It is very difficult to repair any valve in situ without isolating or de-pressurising the system, but for a gate valve or some ball valves, at least you don't have to dismantle and re instate the pipework, which you do for a wafer type butterfly valve. However if you need to do it often it probably means you have the wrong type of valve.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[rit326]

hi

in chilled water system - if provided with expansion chamber/tank at strategic location and properly sized then you will not feel bothered of water hammer.
most of the jerk it will absorb, and the concern about the draining of line while maintenance...there is another method to bypass the valve to be maintained with temporary bypass line otherwise you have to drain the line or just close the particular line with other mean.

and there is no problem of using butterfly valve even in 300-450 mm line in closed loop system.

coz - you have to learn the pattern of water hammer - -how it generated, how it travel, how it multiply , how it dampened etc...
effect in closed loop pipe and open loop pipe.

thanks

 

[rconner]

As a multi-turn valve, a gate valve is far less likely to be involved with water hammer. Quarter-turn valves including butterflies can close quicker, so this question should be considered. It is also true that you can repair a gate valve without removing the valve body from the line. This cannot be done, however, without removing line pressure and evacuating the line. The reason there is a possible disconnect on the advantage of this feature is likely because one may be considering only a flanged applications, and even then it is typically much easier to remove the seating / wedge assembly of a gate valve than it is to remove a flanged and valve body from an existing pipe network. In cases wh​ere the end configuration is anything other than a flange, such as in buried service conditions (e.g. mechanical joint, etc.), the butterfly valve would normally have to be cut from the line and the gate valve would not (in any normally open service an inoperable bfv disk may extend beyond the laying length of the valve, further complicating removal/service).
Other advantages of a modern gate valve over a butterfly valve include the inherent design reliability / durability characteristics of the valve, larger seating surface for greater forgiveness, as well as improved energy consumption. The pumping costs of a butterfly valve, dependent on the assigned flow coefficient of the valves, can be as much as 10X greater (and greater energy consumption etc0. As for throttling, the vast majority of valve applications are simple open and close service. So unless the application is for a modulating service there is no disadvantage ever for a gate valve.

 

[moltenmetal]

Butterfly valves. Worried about sudden opening? Put a gear operator on them.

 

[gerhardl]

If we are talking about 250 to 350 mm valves, you would search for valves with an optimum cost over lifetime value, including the cost for repair and cost/disadvantages for shutdown and maintenance of valves.

In Europe it would be natural to consider butterfly valves of high quality and long standtime, operated by handgear and/or electrical multiturn actuator. Best standtime, closing and and flow conditions would be obtained by double eccentric butterfly valves with flanged connections. Most of rconners considerations (for non-buried lines), such as excessive loss, closing and durability and even non-ability to be operated as end of line valves with-one-sided pressure, will not be valid for a high-quality double eccentric valve.

The actual pressure loss for any valves for any lines can be calculated and taken into consideration if in doubdt. Very often a bad pipeline layout will contribute more than a sensible valve solution.

For systems inside buildings/plants with the linsizes mentioned, the BFL solution would be far more likely to be selected than gatevalves. My recommondation is however the double eccentric, doble flange type.

Nothing wrong with gate-valves. Gatevalves in this size will however be heavier. If you want to motorize the valves it will be far simpler to put a motor an a multiturn gear operator for a BFL valve than on a gatevalve.Sizes of the actuators would be smaller and aand cost far less and less weight and room-demanding.

I would select gatevalves for waste-water and buried lines/actuators.