The valve disk and the spring is a moving part, when the pump turning it open and close for thousand times in a minute, so it tends to wearing. If the valve wore or stuck, the pump pressure will drop down, fluctuates, or pump noisy.
So regularity check the valve can ensure the pump performance and long life
Check valve replacement kit
For triplex pump 15series, 6pcs/kit
For triples pump 18series, 6pcs/kit
Audited Supplier 
){kind=link}