Dont believe that just because the conections to to a water sytem are 1'' that the systems pressure drop and flow requirements will meet your needs. On a Sears system, they have the same valve on thier models. What makes a difference a combination of components:
the valve the tank size the media inside the tank
If you look closely a all the different size systems by the same manufacturer you will see the same valve, same media, but different tank sizes which contains the media, but a different flow rate at a 15 psi pressure drop. Just inside the cover, which gives you access to the storage of salt or potassium, you will see a sticker that shows the service flow rate of the equiptment. For sears it is either 6, 7, 8, 7.6, or 9. This means the the systems were validated at a service flow rate of those values at gallons per minute.(I have spec sheets on Sears and most other systems, except the ones no one knows because of no validation by the WQA but they do have something in comm, the tank size)
So, just because the connections of a valve can be made to any size by a manufacturer. It dosen't mean the system will do the job you would think it would.
Look at this information I recieved from Systematix. They are specialists in Media and Water Treatment Systems.
Expressed by the equation, the relationship between fluid flow through a system and the resulting pressure drop:
Q= k1d2 by the square root of h
Q=flow rate d=size of pipe or system h=pressure drop k=constant for unit conversion
What this says is that the pressure drop for any system is proportional to the square of the flow rate. In other words, if a flow of 1 gpm produces a pressure drop of 1 psi through a given pipe, then by increasing the flow to 2 gpm, the pressure drop would go to 4 psi. By increasing the flow to 4 gpm, the pressure drop would go to 16 psi.
Instead of a pipe, if we have a flow through a water filter of 7.5 gpm and the pressure drop of 15 psi is produced(15 psi pressure drop is the psi rating of sears at the various flow rates), the by increasing that flow to 15 gpm, the pressure drop would go to 60 psi. Increasing the flow to 21.5 gpm would produce a pressure drop of 135 psi (9X). A system rated at 9 gpm at 15 psi pressure drop would go to 60 psi. (thats why most systems installed on homes violate plumbing codes, and you have no water pressure or you have water pressure but there is bleed through and the water dosen't feel soft all the time).
So Code requirements based on upc and ipc requirements of 18 gpm(based if the outside spickets do not have the possibility to run through the system, such as a home plumbed for a water system) for a 2.5 bath home, you can see for larger homes the pressure drop would be greater.
This is one reason Sears systems will not pass a plumbing inspection according to the SBCCI,UPC and IPC Plumbing codes. And why flow rates are so important when you size a system by code.
If anyone has any other questions about any water system just ask. I have been researching water systems and plumbing codes since 1993 and have information from the NAHB, IAMPO, WQA amd other sources in the industry. Water systems, by code, are to be certified by a third party independant testing agency. Just as water heaters, sinks, toilets, pipe, fittings, fauchets, and other components used in plumbing systems are certified to meet code requirements. Don't confuse whole house water systems with appliances, which are end use (use water).