All solenoid valves have a Cv (flow co-efficient) that depends on the design.

Here's some Cv's for 2 way, 1 inch ASCO's (3rd column):

Even the ball valve could or could not be a full port valve. If it's not, there's some flow restriction.

If your system was properly designed, there will be a hydraulic modeling program which uses the automatic operation (solenoid valve) to satisfy the water requirement. The ball valve is a manual over ride in case of solenoid failure, and flow conditions using the ball valve are not important as long as flow exceeds automatic operation.

The hydraulic design would incorporate the specific "K" factor for the valve (again, if properly designed system).

On the other hand, if Cowboy Andy threw together a fire system using parts he grabbed from the seat of his pants, and used engineering from the top of his coconut, there could be an issue here.

Jockey Pump?

First of all, welcome to the site. Second, not knowing your location, I can not say for sure, but most locations that specify fire extinguisher systems require them to be serviced by licensed service people. My best suggestion for you is to contact a dealer or distributer of the components that are labeled in your system. If you have a solenoid valve that is manufactured by XYZ manufacturer, They will know the pressure drop across the valve, and also if the solenoid valve is designed to be used in a fire protection system.

The manual bypass valve you describe could be a simple test provision to see if the flow of water through the system is going to activate a warning device, or it could be a device to manually activate the sprinklers. Again the experts in these systems are the engineers that designed it. If this is a new installation, the blueprints should have the engineer's name on them. If the system is an existing system, try to identify the name of the control panel, and contact them for information on the system. Good luck.

Your flow rate will be determined (restricted) by the size and number of sprinklers and design pressure.

Or to put it in another way , you cannot compare the flow through sprinklers to an almost zero restriction outlet most probably at a lower level than the sprinklers.

Make sure that the correct pressure to the suppliers specification is available at the sprinklers otherwise not enough water is supplied.

The rate of flow restriction depends on type of valve and the manufacturer mechanical design flow characteristics.

Simple physics dictate that a ball valve which has an inside diameter the same size as the conveying medium (pipe-container) has basically negligble (no) flow restriction wheras a solenoid valve of the same size operating via restrictive ports and channels, diaphragm, shuttle plug, etc can in no way approach the same flow values.

Download the IOM for the particular valves you are working with and compare the flow DATA to get the answer.