NPSH available = Atmospheric pressure + static head - liquid vapor pressure - suction piping losses
NPSH required is published by Pump Manufacturer
NPSH available must exceed NPSH required.
There is a national standard for firewater pumps. It is NFPA 20.
I believe all manufacturers must comply.
This pumps generally take suction on an atmospheric tank and discharge about 125 PSIG.
NFPA 20 has a table of capacity (GPM) versus nozzle size.
Measure flange OD and find Nominal Pipe Size...
The pump is cavitating. This is caused by the pumped liquid vaporizing in the impeller. The NPSH available in the system is less than the NPSH required for the pump. Reducing the flowrate reduces the NPSHR (required) by the pump The gravel sound is caused by vapor bubbles (cavities)...
Brittle failure at low temperature is a serious consideration. Brittle failure occurs suddenly and without warning. Pressure containing materials for low temperature service must be ductile. Grey cast iron is brittle at any temperature and should not be used at low temperature. You should use...
It is a question of magnitude. Thrust applied to a motor bearing must be within the allowable thrust load for that bearing. The pump manufacturer should advise you of the pump thrust and the motor thrust capacity.
Both types can be successful but keep in mind that the motor bearing is not...
I am not familiar with this specific pump. However, the angular contact ball bearing is to constrain axial thrust and restrain movement of the rotor. Look for missing snap rings or bearing locknuts that are design to keep the bearing from moving axially. Also try the following contact:
Mrs...
Internal recirculation occurs when operating at flow rates below the Best Efficiency Point. They are eddy currents and represent ineffiency.
The way to avoid internal recirculation is to operate at BEP.
Consider Johnson Well Screens. These are used on raw water intakes for power plants. Screens are T shaped and installed parallel to stream lines. Redundant screens and suction lines are installed to allow one to be cleaned while others are in service. Cleaning is by reversing water flow...
We use air motors from Gast Manufacturing Inc., Benton Harbor, MI Tel: 269-926-6171 Website: www.gastmfg.com
for small injection pumps in hazardous electric areas.
We use Model 4AM-NRV-70C which produces 0.6 HP @ 935 RPM. They have smaller sizes. You will need an air filter / regulator...
Yep,
1. Past operating experience in the same or similiar service per client's Rotating Equipment Engineer.
2. Chapter 5, Pump Handbook, Third Edition, McGraw-Hill
3. Chapter TECH-B, Goulds Pump Manual, 8th Edition
4. Corrosion Data Survey, 6th Edition, NACE International
5. Various...
Tell the builder and the ship owner that you should not operate the pumps off BEP. BEP is the rate that the impeller vane angles are designed for. You should either replace these pumps for 5000 GPM or lower the pumping rate to the BEP of these pumps ~4000 GPM.
One percent margin is acceptable...
You must identify the temperature and pH. Also identify chemical compounds being pumped. There are lots of good materials for chlorines; from FRP to titanium.
One more item.
NPSH calculation are made with absolute pressure not gage pressure. Atmospheric pressure is part of NPSHa. A vertical wet pit sump pump has 14.7 PSIA, 34 feet water column NPSHA to begin with from atmospheric pressure acting on the water surface. To the 34 feet, you add the...
Flowserve is right. A pump can operate with no margin, where NPSH available is equal to NPSH required. There will be some cavitation at this condition as NPSH required is determined at a 3% drop in head which is caused by inception of cavitation.
Following are good centrifugal pump selection...
