SELF-PRIMING PUMPS
START-UP TIPS & TRICKS
A self-priming pump is one that will clear its passages of air if it becomes air-bound and resume
delivery of the pumpage without outside attention. To accomplish this, a charge of liquid sufficient to
prime the pump must be retained in the casing or in an accessory priming chamber. When the pump starts,
the rotating impeller creates a partial vacuum; air from the suction piping is then drawn into this
vacuum and entrained in the liquid drawn from the priming chamber. This air-liquid mixture is then
pumped into the air separation chamber (within the casing), where the air is separated from the liquid
with the air being expelled out the discharge piping and the liquid returning to the priming chamber.
This cycle is repeated until all air from the suction piping has been expelled and replaced by pumpage
and the prime has been established.
Problem:
Not all greases are compatible, even if the grease “types” are the same. Let me say that another way:
Even if the grease types are the same, the greases may not be compatible. Grease consists of mainly two
part: a lubricant (usually oil) and a carrier or base. The bases aren’t always compatible. If you mix
incompatible greases, the result could be shortened equipment life or even catastrophic equipment
failure.
Many facilities choose to use just one or two types of grease. I often hear “this is what we use in all
of our equipment.”This can be bad news if the type of grease the facility is using isn’t compatible
with what the equipment manufacturer originally used.
Looking at one compatibility chart, I was surprised to see that over half (about 57%) of the different
base combinations are either “incompatible” or “borderline.” That takes us back to our 50/50/90 rule:
If you have a 50/50 chance of picking a compatible grease (without doing a little research), 90% of the
time you’ll select one that’s incompatible.
Tip:
Consult the vendor or equipment manufacturer to find out what grease was originally installed in the
equipment. Use the same grease, if possible.
Sometimes, while the bases may be compatible, that doesn’t necessarily mean the lubricant or other
additives will be. You may wish to contact your lubricant vendor to check on the compatibility, once
you’ve found out what is already present in the equipment.
Additionally, people spend a lot of time and effort troubleshooting a pump or other piece of equipment
to determine the cause of bearing failure, without ever checking to see what type of greases have been
used. This information is fairly easy to get your hands on, and it only takes a second to check
compatibility. It might save you a lot of time down the road to check on this up front.
Trick:
Use the Internet. You can do a search for “Grease Compatibility Chart” and come up with a bunch of hits.
Use this chart to find a compatible mix, if you don’t have a supply of the original type of grease the
manufacturer used. I would still check with the grease manufacturer to verify the greases’
compatibility, though. Also, if your equipment is oil lubricated, better check compatibility of that too.
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