Vertical Pump - Heavy Duty Machinery Protection – API670 Monitor
Vertical Pumps, available in various sizes & types, are used in process plants for transporting liquid product. The choice of vertical pumps is often directed by the necessity to raise available NPSH by virtue of the added static liquid head above its impeller. Many times because of limitation of floor area for installation vertical pump is preferred. It also helps in-line piping arrangement allowing piping in any direction besides being its suitability for high pressure service because of its simplified bolting and confined gasket design. However being an overhung rotor design its hydraulic thrust is difficult to balance. Also over the time erosion and corrosion of the impellor occurs. This results in a progressive increase in vibrations due to unbalance of the rotor. If ignored consequential damage to the drive motor’s bearings and coupling will result but often are predictable. Unscheduled failure can threaten personnel and plant safety. The loss of a single line pump can shut down the process causing significant financial losses. A continuous vibration monitoring system will give timely warning to prevent premature plant failure.
A pump’s power consumption often accounts for over 12% of the total electricity used and it is a well recorded fact that an out of balance rotor will consume or waste 15% or more energy.
Faults with vertical pumps are most likely to occur at the time of initial installation and run-in or after overall. Access to the bearings for analyzing and designing a Vibration Monitoring System must take into account the following:
- Bad bearings
- Mechanical looseness
- Hydraulic forces (Cavitation, resonance)
Typical Vibration Sensor measurement Positions
Vibration Diagnostic Chart - Faults common to Vertical Pumps
|1||Unbalance||Proportional to unbalance in radial direction||1 x RPM||Single steady reference mark||Most common cause of vibration. Correct by balancing each rotating parts before assembly then after assembly.|
|2||Misalignment of couplings or bearings. Bent Shaft||Axial vibration 50% of more of the radial level||1 x RPM common but often x 2 or 3 CPM||Single double or triple reference mark||Best identified by dominant axial vibration. Confirm with phase measurement or dial gauges. If sleeve bearing with no coupling misalignment balance the rotor|
|3||Antifriction Bearings||Use Spike Energy (gSE), Demodulation, enveloping or g||High frequency 35K to 55K CPM not related to RPM.||Erratic||Sensor proximity to a defective bearing is a clear indicator. External signals like steam leaks and cavitation can give false readings|
|4||Mechanical Looseness||Often highest in vertical direction||2 x CPM||1 or 2 reference marks depending on frequency. Usually unsteady||Usually accompanied by unbalance and/or misalignment|
|5||Hydraulic Forces||Erratic or pulsating, use velocity measurement||1 x RPM or number of blades on fan or impellor x RPM||Multiple marks , sometimes erratic or fanning||If vibration increases with capacity then cavitation could be the cause. If noise or vibration decreases then problem is probably recirculation. Resonance is most common problem if distinct frequencies are not equal to those described.|
|6||Rubbing||Unsteady large erratic increases||1 x RPM or higher frequencies||Multiple marks erratic, watch for abrupt changes||Likely to occur if shaft is bent or bearings are worn, use noise analysis for high frequencies.|
This IRD Engineered Solution is applied where an API670 Vibration Protection Monitoring System is specified. The IRD8800 monitor is unique in that it can be supplied in smaller racks. This is possible since each module has an individual power supply unit where failure will only lose two channels, not the whole rack. Redundant PSUs are also available. The traditional 19” rack is supplied where multiple machines are to be monitored. The vibration modules are programmable for Velocity Peak or RMS and Displacement Pk-Pk measurements as required. Outputs will be 4-20mA and RS485/MODBUS as well as buffered raw signal for spectrum analysis or Diagnostics On-Line (contact IRD for IRD9900 DOLS). Dual vibration and temperature sensors are available reducing costs and improving bearing detection.
IRD Engineered Solution - Bill of Materials
The vibration protection system for installations with antifriction bearings covers 2 sensors each in radial direction on motor bearing /mounting flange and pump bearing(unbalance, misalignment, bearings, mechanical looseness & aerodynamic forces) The BOM below provides for 4 channels.
|1||Sensor Mounting Pad Mild Steel Blackodized for IRD544M(60x60x16mm) with M6 thread d||4||M60015|
|2||Sensor Inductive Velocity, model IRD544M Classic, On-line measurements, 14-1 KHz, <8% Accuracy, 42.52 mV/mm/s, 260DegC, Class1 Div2 Hazardous Area, Al Enclosure, Note the signal is isolated from the body. Top Exit, Mil 2 Pin Connector. Square base mounting on 4 holes 7.15mm Dia. on 2 × 2 centres, with National Traceable Cal. Cert.||4||M97120|
|3||Cable Assembly General Purpose, Stainless Steel Conduit flexible 5 mm Dia. ID, for IRD sensors to JB or Transmitter. FRLS Shielded 4mm Dia. 5m length, integral to Mil 2 Pin connector and spade lugs at free end. (For Sensor model IRD533)||4||M62107|
|4||Junction Box - Al Di-cast, powder coated, IP65 rated for terminating up to 4x Sensors, supplied with glands and fittings (230x200x110mm)||1||M60047|
|5||Cable Bulk,4 twisted pair, 0.5 Sq. mm., tinned copper, individual pair shielded and overall shielded, PVC, FRLS, Armoured - Price per metre||TBA||M60095|
|6||MONITOR MINI RACK, 2 POS, 5U, PCW 137mm. IRD8800 SERIES - API670 Compliant: caters up to 2 Dual Channel modules. Complete with backplane, terminal strips, RS485 'D' connector and panel bezel. Individual rear mounted dual BNC sockets for TWF buffered output per module to optional Diagnostic On-Line System (Refer to IRD9900 DOLS).||1||M88002|
|7||MONITOR M88200 ABSOLUTE CASE VIBRATION MODULE, IRD8800 SERIES - 2 CHL, VEL INPUT - Dual Channel Bar-Graph with bright LCD and Digital display and Warning, Alarm & Startup LEDs. Complete with individual SMPS 90-270V AC, 50/60Hz,1Ø.||2||M88200|
|8||Cabinet / Panel, for VMS, wall mounted, IP55, (H)600mm x (W)800mm x (D)600mm, fully wired for supplied modules.||1||M68701|
Taking you Further
Most online vibration protection systems are limited to measuring only overall vibration levels and hence alarming. It is always beneficial to undertake a FFT frequency analysis from the raw signal at the BNC sockets on the monitor system. IRD Mechanalysis provides consultancy services as well as a range of state of the art diagnostic analyzers and meters.