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?

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.

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