Assorted lot

[Hydros]

Here we have from left to right:

PARKER SLOW DOWN
P/N MV-600S
1/2" ID PIPE THREAD

PARKER CHECK VALVE
P/N C800S
3/4" ID PIPE THREAD
RATED 5000PSI
15 GPM

PARKER FLUID CONTROL VALVE
P/N F800S
3/4" ID
RATED 5000PSI
15 GPM
(appears this can be used as a check valve, a slow down or as a shutoff)

GAR CHECK VALVE
P/N 8LV0121
#12 JIC
RATED 3000PSI
CRACK PRESSURE 250 PSI

[Lifted Monte Carlo]

So........ items #1 and #3 operate in basically the same fashion......control the flow of fluid?

[Guest_Hydros]

Well, #3 is like a combination of #1 and #2

All three control fluid flow in some way.
#1 shuts it off and controls the flows.
#2 controls flow for only one direction
#3 does what 1 & 2 do. Think of it as a check valve that will allow reverse flow when you open the valve. This could be useful if your dump valve locked up.