Hydrolyzes pyrophosphate formed during P-Ser-HPr dephosphorylation by HPrK/P. Might play a role in controlling the intracellular pyrophosphate pool. diphosphate + H2O = H(+) + 2 phosphate Belongs to the HAD-like hydrolase superfamily. PpaX family. Was originally (PubMed:9465101) called P-Ser-HPr phosphatase as it has been shown to stimulate P-Ser-HPr dephosphorylation, but actually (PubMed:12359880) it has pyrophosphatase activity.