Define the capacity improvement you need
Distinguish increased output from lower flux per square metre and capacity during maintenance. These objectives can call for different arrangements. Adding modules at the same overall flow reduces the calculated average flux; increasing flow as well requires a utilities review. Record the net demand, operating hours, temperature and feed conditions that justify the expansion.
Compare the current and proposed layouts in a simple schedule: module count, area per element, banks and simultaneous operating steps. Identify retained and replaced equipment. Documented rack arrangements apply to their specified geometry and components. Calculate the new distribution using the actual circuit being expanded, and make the intended operating configuration part of the quotation basis.
Check the hydraulic resistance of each flow path
Total flow divided by the number of modules is an average, rather than an individual measurement. Pipework, fittings, valves and connections add resistance between the common supply and each element. Differences in those paths or in membrane condition can change the distribution. Include the filtrate manifold in the hydraulic review, since it is part of the same flow path.
The expansion calculation needs internal pipe diameters, lengths, elevations, fittings and pump curves. Check available pressure at the least favourable locations against component limits. Where new and used modules share a bank, assess permeability differences as well. Common feed and filtrate pressure readings describe the assembly but may conceal differences within it. Decide what additional observations are needed to verify distribution.
Calculate backwash demand before ordering modules
Consider an illustrative example that does not represent a commercial model: twelve 60 m² modules provide 720 m². At an assumed filtration flux of 50 L/(m²·h), gross filtration flow is 720 × 50 / 1000 = 36 m³/h. At an assumed backwash flux of 100 L/(m²·h), washing all twelve together needs 72 m³/h for the duration of that step.
Washing two groups of six reduces instantaneous demand per group to 36 m³/h but changes the sequence and available production time. These assumptions explain the arithmetic only. Use the backwash intensity in the approved module documentation, and calculate net output with the time and water volume used by every operating step. Check storage volume as well as pump flow.
| Service | Expansion check |
|---|---|
| Feed | Pump curve, prescreen and flow per bank |
| Filtrate | Manifold, backpressure, storage and water destination |
| Backwash | Instantaneous flow, pressure, usable volume and simultaneous groups |
| Air, where applicable | Approved flow, pressure and distribution per module |
| Drainage and CIP | Waste capacity, liquid volume, circulation and isolation |
Review partial operation and transitions
A rack does not always operate with every module filtering. Assess start-up, backwash, chemical cleaning, one isolated bank and return to service. State the available module count and permitted flow in each condition. Controls must prevent full demand being imposed on reduced membrane area without respecting the allowed flux and pressure.
Check filling, venting, valve timing and pump ramps. Changes to liquid volume or pipework can affect transitions between steps. Define how a module will be isolated for intervention and how chemical-cleaning circuits remain separated from useful water. Reflect these decisions in both the P&ID and the operating description so the mechanical and control arrangements agree.
Request a proposal with clear supply boundaries
Separate membranes, frame, manifolds, adaptors, instrumentation and control changes in the scope. For a module-only order, identify who verifies the circuit and who modifies the control system. An itemised supply list supports meaningful comparisons and avoids attributing an existing installation bottleneck to the new membrane elements. State any interfaces that remain for the site team.
Agree post-installation checks covering leaks, sequences, flow, pressure and water quality under specified conditions. Record the active bank arrangement and temperature alongside each reading. Acceptance should confirm the expansion objective selected at the outset, with net output and utilities that can be sustained under the intended operating schedule. Retain the results as the new operating baseline.
Common questions
Can an expanded rack use the existing pump?
Check its curve against the changed circuit. It may be possible to retain flow while lowering membrane flux; increasing output requires a new operating-point assessment.
Can new and used modules share a bank?
Assess compatibility, hydraulic-resistance differences and how flow will be checked and controlled. A common manifold does not guarantee uniform distribution.
Is backwash demand calculated from filtration flux?
No. Use the product's specified backwash intensity, the membrane area washed simultaneously and the hydraulic requirements of the full cleaning sequence.