When to use "pump control cone valves"? 2

[gustorf]

Most of the American water works have "pump control cone or ball valves" acting also as a check valves behind their pumps. In Europe the standard seems to be a non slam nozzle check valve plus an isolation gate or butterfly valve. -which seems to be the less expensive design.
Can anyone tell me the reason when to choose the cone valves and when to choose check valves?
Can I simply replace a cone valve by a check and butterfly valve?
Hans

 

[hydrae]

Gustorf

Is the 'cone' valve acting as a pressure reducing valve?
Most installations I am famialar with use a diaphram operated globe valve such as Cla for pressure control unless the pump is on a drive.
The configuation of the control valve can provide a whole list of pressure and flow control functions depending upon the installation.

Hydrae

 

[gustorf]

Hydrae,

I think its not pressure control.
The cone valves are mainly APCO 2200 and to be used for starting up the pumps against the closed valves and smooth opening. The hydraulic actuator shall close the valve fast at reverse flow.?

Hans

 

[hydrae]

Gustorf

AWWA butterfly valves do not do well in high velocity throttle applications, even for the short duration of pump startup, a tricentric or other metal to metal seat may be ok but then the price goes up and you lose the resilient seat...
If the system does not have a no slam check now, surge control would be the issue in a pump control valve function, which resolves all normal operation surges (but does not fix a surge from a loss of power)

Hydrae

 

[bimr]

It depends on the hydraulics of the application. The fluid velocity, the numbers of start-stops of the pumps, the number of pumps, the size of the water distribution system, and the pressures in the system all have an effect on the hydraulics.

Opening, closing or regulating valves or pumps starting and stopping, usually causes surges in pipelines carrying liquids. These surges, also called hydraulic transients may range in importance from a slight pressure or velocity change to sufficiently high pressure or vacuum to rupture the piping system, to damage pumping equipment and cause extensive shutdown time. Water hammer, a result of hydraulic transients, will occur when the total surge pressure exceeds approximately twice the value of the static pressure in the system when the fluid is at rest.

Detailed pipeline surge analysis by an expert should be considered under the following design conditions:
(1) Generally, if the interaction of pump station, piping system, valves and control system is complex case following a power failure or during startup.
(2) If power failure at the pump station would result in significant reverse flow, which can check valves or causes a fluid rejoinder surge. In a system with a flat pipeline profile, reverse flow are usually not significant. In a system where the pumps work against a significant static lift, surge pressures can be many times the maximum steady state operating pressure.
(3) If the pipeline profile has significant intermediate high points where the fluid may separate, following power failure, and result in high surge pressures upon rejoining.
(4) If the pump station or individual pump intake suction through a pipeline of significant length (several hundred feet) a power failure may result in high-pressure heads. For pumps located immediately adjacent to storage tanks, suction line pressure transients are usually insignificant.
(5) If the pump station is equipped with discharge check valves and air vessels, the check valves may be slammed shut by the air vessel or parallel-connected pumps following power failure.
(6) If the preliminary calculations indicate that surge control equipment is required in the system, optimum performance and surge control equipment selection can be established through detailed surge analysis. Surge control system analysis should generally be performed for vertical turbine valve installations and any pump installation where individual pump capacity exceeds 500 gum.

Pump control valves function as part of a surge control system including valve, power and manual valve, operators, accumulator, sensing and recording devices. This system automatically prevents water hammer in starting and stopping of pumps should include safety features in its design to prevent damage from malfunctioning equipment.

If you have no concerns at all about surge pressure or water hammer, then go ahead and use the check valve and butterfly.

If you have concerns about surge pressures or water hammers with the starting and stopping of pumps, then you would want to use the pump pressure control valves. The pump pressure control valves are the "electric check valves", and the rotary ball valves ("cone valves").

Pump pressure control valves are mainly used to regulate out the pressure surges that occur in starting and stopping of pumps. The pump pressure control valves will remain closed during pump startup until the pump discharge pressure reaches the valve’s set-point. This minimizes pressure fluctuation when the pump goes online.

When the pump shuts down, the pump pressure control valves close slowly (unlike a check valve). The slamming of a check valve may cause a water hammer. During an emergency such as a power failure, the pump pressure control valves will have a rapid controlled closing which will also tend to minimize pressure surges.

The cone valves can be optionally automated in order to control pump discharge pressure. If you are concerned about headloss through the valves, the cone valves are used because the pressure drop across the valves is minimal.

Here is an interesting article on the failure of a valve:

http://www.capitalcentury.com/1975.html

 

[gustorf]

bimr,

thank you for the excellent article.

Non slam nozzle check valves like Noreva valves should prevent the backflow water hammer risks.

Geoff Stone of Design, Detail and Development wrote another interesting article about pressure transients. You may get a copy at blenrayaust@yahoo.co.uk
He has posted a lot of interesting things in this forum.

 

[cchung]

I'm new to process control valves. Apart from their physical appearance, what is the difference between a ball valve and a cone valve? Reading some product brochures, it appears the mechanics of flow control are similar (a rotating unit with a straight-through opening, whose angle at any given time determines the aperture size from full bore to closed).

Also, can globe valves be used in place of a cone valve or ball valve in a transient control situation, or are they really suited more as alternatives to gate valves?

cchung

 

[stanier]

bimr,

Classic pints about waterhammer.

One thing not mentioned is the maintenance required of the elctric or hydraulic operated devices. If the maintenance and testing is not carried out then they dont work. A spring operated non slam check valve is far more reliable.

In these days of economic rationalism maintenance budgets are squeezed, engineering resources are reduced and the deives may not be as reliable as once thought.

A risk assessment study should be done before any surge analysis. "Failure to maintain" is one big button pusher when it comes to equipment. Unfortunately pump control or check valves that fail to operate can cause as much damage as a relief or safety valve that doesnt operate. Yet relief/safety valves are required by legislation to be registered and calibrated BUT NOT pump control/check valves.

Give me a check valve of non slam characterisitics any day. Then I am fussy and want an annulus type.

see paper on

http://www.pipingdesign.com

on surge risks