The check valve maintains system pressure at the injector rail to prevent vapor lock and improve hot starts.

If your pressure is low I'd suspect the fuel pressure regulator, fuel filter and fuel pump, pinch/crush fuel line in that order before suspecting the check valve. If the residual pressure is low or drops too fast suspect a leaking injector or FPR, or bad check valve.

With the gauge in place and the pump running, gently pinch off the return line (the short piece of rubber hose just past the FPR). The fuel pressure should rise. That will confirm if your pump is capable of at least 43psi. Don't pinch the line too much as I don't think it can withstand full pump pressure without bursting or blowing the end of the hose off; pinch it just enough to confirm a rise in pump pressure.

Also confirm that applying vacuum to the FPR causes a decrease in fuel pressure. And you might want to do a pump volume test.