Assuming you are speaking of diaphragm with guided disc type:

1 - If valve is feeding into an open downstream system where system resistance curve is low, if the valve is closing tight against very low downstream pressure, if there is a high pressure differential across the valve,  then the valve closing speed curve will lengthen and flatten out (longer close time, more linear closing rate).  All this is due to the fact that the ratio between entry and exit "chambers" is different based on what direction the water flows in.  High differential pressure across a diaphragm valve can cause the diaphragm supported disc to collapse against the seat at the end of the stroke because hdraulic support under the digphragm from downstream pressure is lost "exponentially" on an open system.

2 - As far as modulating the valve will behave similar in either direction with differences large and small depending on system conditions.

Describe the application and system conditions, show us the system curve if you have it.

PUMPDESIGNER

that information is usually provided by the valve manufacturer. the generally use flow testing to determine the flow up/flow down characteristics of the valve.

Ask for a bi-directional valve, this may change the design of the valve i.e. balanced plug etc. then the CV will generally be the same. Only baffle plates and the like will limit this.
Br
B

As a further question, how is the reading affected if a flow meter that is supposed to be vertically mounted (ie mounted on a vertical piece of piping) is horizontally mounted?

cssvas, You've made a major capital investment in a high tech/high performance control instrument, that has been specially designed by a CV maufacturer. Why would you want to install it backwards and waste that investment? If this is a field problem and wasn't caught in the instrument ring-out, I hope the control set was set up in a standard ISA control valve station set-up. If so, open the by-pass close the blocks, bleed it off and rotate the valve so that the flow is entering the inlet flange.

If the above isn't do-able, contact the Manu'f. for the tech data on reverse flow through the valve, if they have it. They will in all probability tell you to reverse the valve.

Godluck.
saxon   

mashiz, Chek with the manu'f.. Some flow meters require proper orientation in the gravitational field or require flow induce vibrations based on piping orientation, in order to operate correctly. Some types of flow meters that come to mind are, variable area flow meters like rotameters or coriolis mass flow meters.

Hope this helps.
saxon