How to Troubleshoot Low Pressure Issues in Ebara Vertical Pumps

Low pressure is one of the most common operational complaints in vertical multistage pump systems. It can affect booster sets, HVAC circulation, irrigation, RO plants, and industrial water systems.
In most cases, the pump itself is not faulty. Low pressure usually results from suction problems, control issues, system changes, or installation and maintenance errors.
This guide provides a logical, step-by-step troubleshooting approach to identify the root cause and restore correct pressure.

1. Verify That Low Pressure Truly Exists
Before adjusting the system, confirm the problem is real.

• Check that pressure gauges and sensors are accurate and calibrated
• Compare pressure at pump discharge with pressure at end points
• Confirm the issue is system-wide and not limited to one zone
• If a VFD is used, confirm the pump is running at the commanded speed

Incorrect instrumentation is a frequent cause of false low-pressure alarms.


2. Check Pump Speed and Electrical Supply
Pump pressure is directly related to rotational speed.
Inspect the following:

• Confirm correct motor rotation direction
• Verify supply voltage and phase balance
• Check VFD output frequency and ensure it reaches rated speed
• Confirm minimum speed limits are not set too low
• Ensure no energy-saving or night-setback mode is active

Even a small reduction in speed can cause a noticeable pressure drop.

3. Inspect Suction Conditions
Poor suction is the most common cause of low pressure.
Check for:

• Low water level in the suction tank
• Blocked or dirty suction strainer
• Air leaks at suction joints or flanges
• Undersized suction pipe
• Excessive suction pipe length or too many bends
• Partially closed suction valves

If the pump cannot receive adequate water, it cannot generate pressure.

4. Look for Air Entrapment
Air in the pump or pipework reduces hydraulic efficiency.
Possible causes include:

• Inadequate venting during commissioning
• High points in piping without air release valves
• Loose fittings allowing air ingress
• Incomplete priming

Bleed air from the pump casing and ensure automatic air vents are installed where required.

5. Check the Discharge Side
Restrictions or losses on the discharge side reduce delivered pressure.
Inspect:

• Discharge isolation valves fully open
• Check valve stuck or installed incorrectly
• Pressure relief valve opening prematurely
• Leaks in piping, joints, or flexible connectors
• Bypass lines left open

A pump may be producing pressure internally, but the system may not be retaining it.

6. Compare Operating Conditions With the Pump Curve
If the pump operates far from its design duty point, pressure will drop.
Consider:

• Has system demand increased since installation?
• Have new floors, zones, or outlets been added?
• Is the pump oversized and operating too far right on the curve?
• Is excessive throttling used to control flow?

If system conditions change, pump performance must be re-evaluated.

7. Inspect Internal Pump Components
Internal wear reduces pressure gradually.
Check for:

• Worn impellers or diffusers
• Internal leakage between stages
• Shaft sleeve wear
• Excessive bearing clearance
• Mechanical seal damage causing internal bypass

These issues usually appear after long service or poor suction conditions.

8. Identify Cavitation Symptoms
Cavitation reduces pressure and damages components.
Warning signs include:

• Crackling or rattling noise
• Fluctuating pressure
• Increased vibration
• Rapid seal wear

If cavitation is suspected, review NPSH availability, suction layout, water temperature, and suction losses.

9. Review VFD and Control Settings
Control system errors frequently cause pressure complaints.
Verify:

• Pressure sensor location and calibration
• Pressure setpoint values
• PID control tuning
• No conflicting commands from BMS or PLC
• Correct operation of sleep or standby modes

Incorrect control logic can limit pressure even if the pump is mechanically sound.

10. Assess System Demand
Sometimes the pump is performing correctly, but demand exceeds design.
Consider:

• Peak usage higher than original design
• Seasonal irrigation or cooling load increase
• Fire system testing affecting pressure
• Multiple zones operating simultaneously

If demand has increased, the solution may be additional pumps, zoning, or system redesign.

11. Quick Field Diagnostic Sequence
When time is limited, check in this order:

1. Verify gauges and sensors
2. Confirm pump speed and rotation
3. Inspect suction water level and strainer
4. Bleed trapped air
5. Check discharge valves and leaks
6. Review VFD and control settings
7. Compare operation to pump curve

This sequence resolves most low-pressure cases efficiently.
Low pressure in Ebara vertical multistage pumps is usually caused by system conditions rather than pump defects.
By methodically checking suction conditions, pump speed, controls, internal wear, and system demand, pressure problems can be identified and corrected quickly.
Proper installation, correct VFD integration, and routine maintenance are the best ways to prevent recurring low-pressure issues and ensure reliable long-term pump performance. ​For more info contact Ebara Pump Suppliers in UAE or call us at +971 4 2522966.

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