Common System Pump Startup Problems
Improper installation causes most metering pump startup problems. These suggestions help ensure proper selection and installation of a chemical feed pump or chemical feed system. If you have any further questions, contact one of our experts for assistance.
Factors to consider when choosing a pump:
- What type of system will use the pump? Schools or hospitals may consider economy more important. Industrial applications may focus on ruggedness and other features. For pumps in a hazardous location, take care in choosing components like the motor.
- Consider the location of the injection point within the system. Allow for convenient access. Note any extreme temperatures (like sun exposure or freezing) to plan for.
- For proper operation, the following should match your application. Our experts can advise you if you’re unsure of what you need.
- Flow rate
- Materials of construction
- Pump size
- What method of control will it use? Manual continuous operation; on/off operation; or, proportional to some process signal.
- What container will hold the chemical? A new tank or an existing tank? A day tank or a bulk-shipping container?
- Locate the pump near the feed tank. Keep the suction line short. Metering pumps will “push” against great pressures, but they won’t “pull” for great distances.
- Limit the total length of the suction line to 3 feet suction lift or 6-7 feet flooded suction. Use an adequate-sized line. Minimize bends, elbows, or other restrictions.
- Flooded suction is always preferred, easier to prime, and more “forgiving.” Use flooded suction for fluids such as alcohol where the vapor pressure could be less than the suction lift.
- When piping the system, be aware of the location of the valves, unions, flanges, compression fittings, etc. Are they easily accessible?
- What accessories will you use with your pump? (more tips on this below!)
- What size of pipe and accessories will you use? (more tips on this below!)
Pump Startup Problems – Consider the Accessories
Suction Strainer – Always use a suction strainer, 40-60 mesh to prevent foreign matter from getting into the ball checks of the metering pump.
Isolation Valves – Provide on both suction and discharge for ease of maintenance. Select large port quick opening valves. A ball valve has a generous opening and is easily stroked from full close to full open position. A needle valve would not be an acceptable suction valve, as it would pose a restriction. Plus, it’s not obvious when a gate or globe valve is fully opened or only partially opened.
Calibration Column – The pulsed flow of positive displacement metering pumps makes a suction draw down column the best method to measure pump performance. Plus, the fact that metering pumps are often used in very low volume applications makes this more important.
Pulsation Dampener – Always discuss the requirements and goals of pulsation dampening with the manufacturer. Provide the reason for dampening and the degree of dampening required. Long pipe runs between the pump and injection point may need pulsation dampeners to reduce water hammer or pressure spikes caused by acceleration of the liquid in the discharge line.
Pressure Valves and Gauges
Relief Valve – Does the pump have an internal relief valve? Will the system require an external relief valve in addition to the internal relief valve?
Back Pressure Valve – Required when a system does not provide backpressure and the pump does not contain a backpressure device.
Note: A partially closed valve is not an acceptable back pressure regulator. Proper back pressure requires a spring-loaded, diaphragm-type back pressure valve. Always use a back pressure valve when feeding from a bulk tank to an injection point with little or no back pressure. Do not depend on spring-loaded pump valves for this application. Use back pressure valves when a low-pressure injection point is hydraulically lower than the feed tank. If you don’t install a back pressure valve, fluid can siphon. Plus, the pump rate may be erratic, often pumping at a rate higher than the actual dial setting.
Pressure Gauge – Is a gauge required? Use a snubber on the gauge for pulsating services. Use a diaphragm seal for chemicals that are corrosive to the stainless steel gauge parts. Also, use them for chemicals that are very thick or contain particles that could clog the Bourdon tube within the gauge.
Selection and Sizing the Pipe and Accessories
Suction Piping – The single, safest rule of thumb for selecting suction pipe size is to use one size larger than pump suction connection. Piping may be the same size as suction connection for slow speed pumps used with low viscosity chemical. As a practical matter, do not use hard piping smaller than 1/2″. For low pressure, low temperature, low flow applications which use tubing, 3/8″ is a practical minimum size.
Discharge Piping – Take care to select or specify piping suitable for the discharge pressure. Discharge pipe size is not as critical as the suction pipe size. Matching the pipe size to the discharge connection size is sufficient. Keep in mind the practical minimum size of 1/2″ for pipe and 3/8″ for tubing.
Calibration Columns- Size columns to allow at least a one-minute test. Lower capacity pumps may be better served by a two-minute test. Use a tall, thin column for ease and accuracy.
Pressure Gauge – Choose gauge sizes 30% to 50% larger than maximum expected pressure. Caution-consider the relief valve pressure, not the operating pressure. Example: A 150-psi gauge would adequately serve a 100-psi injection service, however, a 100-psi application with a 150-psi relief valve would require a 250-psi gauge.
Relief Valves – Size at 50 psi or 10% above the normal operating pressure. Use whichever figure is greater. Most pipe the relief valve return back to the tank. Most also prefer transparent return tubing over hard pipe. That’s so that when the relief valve opens, you can observe fluid in the line.
Back Pressure Valves – Set valves to provide a minimum of 50 psi.
Avoid Pump Startup Problems – Evaluate Your Installation
When replacing equipment, question the existing installation.
- Will your program operate at the same feed rates as the previous program?
- Is the equipment properly sized for your products?
- How well has the equipment been operating?
- Any problems with reliability, accuracy, unusually high maintenance requirements?
There is no better start to a new chemical feed program than to ensure that trouble-free equipment delivers the chemical accurately. The best method to avoid problems with chemical feed equipment is to properly select the size and type of equipment from the beginning.