I am installing an orifice in a system with a check valve. A far as flow is concerned in relation to the cracking pressure of the check valve, does it matter if I put the orifice upstream or downstream of the check valve? If I put the check valve upstream of the orifice, then I think it is possible that I will not get the necessary delta P across the check valve to ensure the valve remains open (it may reseat due to the low delta P and then start chattering). If I put the check valve downstream of the orifice then I should not have a concern with check valve cracking/seating pressure. Does this sound logical?

I know there are alot of other system parameters that affect this but I was looking for a general rule of thumb or typical installation configuration?  

The introduction of an orifice in the system increases the dP across the orifice by reducing flow in the entire branch, therefore all points upstream of the orifice will tend to increase in pressure and all points downstream will tend to decrease in pressure.  The differential pressure in the branch is increased with an orifice installed.  Now the same flow in the branch occurs at a higher differential branch pressure, although the differential cracking pressure of the check valve remains the same.  No change as far as the check valve hydraulics is concerned, but since branch inlet/outlet pressure is greater, there's a chance it might need a new pressure rating, if the net effect is to increase upstream pressure and the check is installed upstream of the orifice.

The check valve only sees its dP across itself, the check valve.  It does not see the dP across the orifice, nor does it see the dP from beginning of branch to end of branch, so it doesn't really care where it is located in relation to the orifice, as far as what affects its opening or closing differential pressure.  The cracking dP across the valve remains the same.  When ... it sees that dP, and opens or closes, is another story.

So now the question becomes, how will the reduction of flow in the branch by the addition of an orifice affect the operation of the check valve?  Starting from a lower pressure upstream of the check valve, the reduced flow in the upstream branch segment will delay the opening of the check valve, since at reduced flow it will take longer for the upstream piping to reach the cracking pressure at the check valve.  Beginning with a higher pressure upstream of the check, reduced flow would tend to keep that pressure higher for a longer time and tend to keep the valve open longer.  

In the same manner, pressure in the downstream segment of the branch is also at reduced flow, so pressure changes there are slower too.  The check would tend to open later, since reducing pressure downstream would tend to take a longer to reach and it would tend to stay open longer, since increasing pressure downstream would take longer to reach the valve at reduced branch flow.  The net effect is, branch differential pressure increased and time constant of the branch pressure change response to flow change is increased.  

Chattering is a transient response and depends on how fast the piping upstream of the check valve changes pressure in relation to how fast the downstream segment changes pressure.  When the whole differential pressure in the branch is relatively small, chattering occurs.  A relatively large differential branch pressure (much greater than check valve cracking pressure) and a consequently more sustainable flowrate in the branch will tend to avoid chattering.  An orifice, increases branch differential pressure, but decreases flowrate, hence it may or may not be effective in reducing chatter.  In cases where it is not effective, consider using a preloaded check valve.

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