They should flow air through them in either direction. It's easier to blow air into the pushrod seat and you should feel air coming out the feed hole. I had several used hydraulic lifters laying around, both roller and flat and that is how I determined I had a bad one and that the replacements were also bad.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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