Comparing fully automatic filter press quotes starts with forcing every offer onto one written duty basis: slurry source, feed solids concentration, daily dry-solids load, operating hours, feed variability, required cake condition and where the filtrate goes. Only after that basis is fixed does price mean anything, because two presses quoted against the same hourly feed volume can be sized for very different solids loads. The deciding conditions are physical ones you can measure or define — dry solids per day rather than slurry cubic meters, the complete cycle time rather than the filtration step, and the list of automation functions actually supplied rather than the word “automatic” on the cover page.
Put Every Quote on the Same Slurry and Duty Basis
Reissue a single comparison basis to every bidder before you read a price. That document states the slurry source, feed solids, daily dry-solids load, operating hours, how much the feed varies across a shift or a product change, the cake condition the downstream handling requires, and the destination of the filtrate — discharge, reuse in the plant, or return to a clarifier.
The reason is arithmetic rather than preference. A filter press fills chambers with solids, so the volume of chambers you need follows the mass of dry solids per batch, not the volume of slurry pumped. A quote written against 20 cubic meters per hour of “wastewater” at one assumed solids concentration and a quote written against the same flow at half that concentration describe two different machines. The cheaper offer may simply have assumed a thinner feed, which means fewer chambers and less useful treatment capacity for the same stated duty.
Feed variability deserves its own line because it sets how the press behaves at the limits rather than at the average. Ceramic and stone plant effluent shifts with product changes, glaze line washdowns and polishing operations, so a daily average solids figure can conceal a peak the press has to absorb within the same operating window.
Where the plant genuinely has separate duties — a polishing water circuit and a dilute glaze recovery stream, for instance — do not force them into one basis. Different feeds with different required endpoints belong in separate comparison groups, each with its own duty statement, even if one supplier eventually serves both.
Compare Tested Output Over the Complete Press Cycle
Treat a promised throughput or cake dryness as unverified until it comes with trial data on representative slurry and the complete cycle behind it. The US EPA’s biosolids technology fact sheet on recessed-plate filter presses, written for US municipal biosolids practice, describes representative testing as part of how these batch presses are specified and evaluated; the principle carries to industrial slurries even though its performance and cost figures do not.
A filter press is a batch machine, and daily output is batches per day multiplied by the dry solids retained per batch. The filtration step is only part of a batch. Ask for the cycle broken into filling, filtration, any membrane squeeze step, opening, cake discharge and the time allowance for cloth cleaning. A supplier quoting a short filtration time and a long plate-shifting and discharge sequence can deliver fewer batches per shift than one with slower filtration and faster mechanical handling.
Cake dryness without its conditions tells you equally little. The same press produces different moisture from different feed solids, filtration pressures, squeeze pressures and cycle lengths, and a very dry cake achieved by extending the cycle costs batches. So record the test feed alongside the measured cake moisture, the filtrate clarity, the pressure used and the elapsed cycle, and compare offers on that whole set.
A membrane press adds a squeeze step that compresses the formed cake after filtration, which can lower moisture further but also lengthens the cycle. Whether the benefit is worth the step depends on the slurry’s compressibility, so for a compressible ceramic or stone sludge it is a question for the trial, not a specification you assert in advance.
Budget-stage offers can legitimately stay provisional. Treat them as provisional in writing, with the missing performance basis named and an agreed trial identified as the thing that closes it, rather than letting an indicative figure harden into a comparison input.
Separate Automation Functions from Operator Work
“Fully automatic” is a marketing label covering several independent functions, so list them separately and record for each one what equipment the supplier includes and what the operator still does. The functions worth itemizing are plate closing and pressure maintenance, feed pump control and sequencing, filtration endpoint control, plate shifting, cake release, cloth washing, and fault recovery when a cycle stops part way.
Automatic plate shifting and reliable cake release are different problems. A shifter moves plates apart so cake can fall; whether the cake actually releases depends on the cloth, the cake’s moisture and its adhesion to the fabric. Met-Chem’s technical guidance on plate shifters and its Super Shifter describes distinct plate-shifting arrangements together with operator checks on cake discharge — a useful illustration that an automated shifting mechanism is specified alongside operator observation, not as a substitute for it. That is a description of one manufacturer’s product family and says nothing about what another supplier’s shifter will do with your cake.
Fault recovery is the function most often left out of the comparison and the one that decides staffing. If a plate fails to close, a cake bridges in the discharge chute or the endpoint sensor disagrees with the feed pump, ask what the control system does and what an operator must do. A press that pages an operator for every incomplete discharge is not unattended, whatever the data sheet says.
An attended line is a legitimate choice. A deliberately manual or semi-automatic press can suit a plant with existing shift labor and a predictable schedule, provided the labor and operating hours are priced openly in the comparison rather than silently absorbed. The failure mode to avoid is buying an “automatic” press on the assumption of unattended operation and then discovering the planned staffing cannot cover the manual steps that remain.
Add Utilities, Cleaning and Site Scope to the Price
Scope boundaries move prices more than plate area does, so mark each supply item as included, excluded or optional and name who is responsible for the interface. The items to run through are the press itself, feed and conditioning equipment such as sludge pumps and polymer or coagulant dosing, utility packages including compressed air and hydraulics, cake handling under the press, the support structure and access platform, site connections for power, water and drainage, installation, and commissioning.
Cloth cleaning is where scope quietly transfers to the buyer. One quote may include an automatic wash manifold with its own pump, water connection and drainage; another leaves cleaning to operators with a hose. Compare them as separate scope items covering the wash equipment, the water supply and its pressure and quality requirement, where the wash water drains and whether that drain returns to the clarifier, the physical access needed to reach the cloths, and the operator time the supplier expects between washes.
Cloth condition is not a housekeeping detail. A blinded cloth raises the filtration pressure needed for the same flow, lengthens the cycle and makes cake release less reliable, so cleaning scope feeds directly back into the throughput you compared. Met-Chem’s filter cloth washing guidance sets out cloth-plugging indicators and alternative cleaning arrangements together with the connections, drainage and operator work each one brings; it also makes the point that cleaning method and materials depend on the specific cloth and the specific foulant. That matters when an automatic wash is offered as standard: if the cloth and the foulant in your slurry call for a different supplier-approved cleaning method, the offered wash system may not be the one you need, and the supplier should say which method applies to the cloth being quoted.
Existing plant equipment can of course be reused — a feed pump, a sludge holding tank, an air compressor — but only after its capacity, current condition and compatibility with the new control system have been checked. Record who performs that check, because an assumption of reuse that fails during commissioning becomes an unbudgeted site cost at the worst moment.
Compare Operating Costs and Commercial Commitments
Once two or three offers are technically suitable, estimate annual running cost for each on one shared operating schedule, using assumptions the trials support. The cost lines are polymer or coagulant consumption, electricity for the feed pump and hydraulics, wash water, wear parts including cloths and plates, cleaning labor, scheduled maintenance, and cake disposal.
Cake disposal is usually the line that reorders the ranking, because a wetter cake means you pay to transport and dispose of water. The tonnage leaving the site is set by the dry solids plus the retained moisture, so a cake moisture difference that looks small on a data sheet multiplies across every truck for the life of the plant. That is also why the cake condition in the duty basis should reflect what the disposal route or reuse application actually requires, not an arbitrary target.
Keep uncertain inputs visible as alternatives rather than resolving them in a supplier’s favor. If one bidder claims lower polymer dosing but the trial did not test it, carry both the claimed and the current dosage as two scenarios and show which one changes the ranking. Assigning unsupported savings to an offer is how a comparison stops being a comparison.
The commercial side needs the same discipline. For the preferred quote, record the test feed and measured outputs with the operating conditions they were achieved under, who supplies and connects utilities, who performs installation, the acceptance basis that will be used at handover, the lead time, the warranty period and what the service scope excludes. A performance promise and the obligations that deliver it have to sit inside the same defined boundary before the final commercial total means anything. Where the handover includes operator training and acceptance checks, those belong in the delivery scope of the quotation rather than being arranged afterward. Early budget screening can leave several of these open, as long as the offer is not then treated as a compliant bid.
Build a Bid Sheet That Exposes Exclusions
| Élément de comparaison | Common basis | Evidence or scope to record for each supplier | Unresolved item to carry forward |
|---|---|---|---|
| Slurry and treatment duty | Slurry source, feed solids, daily dry-solids load, operating hours, variability, required cake condition and filtrate destination | The feed and duty assumptions used in the offer | Separate genuinely different duties into different comparison groups. |
| Tested output and cake condition | Representative slurry trials and the complete cycle: filling, filtration, any squeeze step, opening, discharge and cleaning allowances | Test feed, measured outputs, operating conditions and the cycle basis behind the promised output or dryness | Keep preliminary performance provisional until an agreed trial closes the missing basis. |
| Automation and staffing | Plate closing, feeding, endpoint control, shifting, cake release, cloth washing and fault recovery considered separately | Included equipment and remaining operator actions for each function | Record manual work and its labor and schedule implications; automatic shifting does not establish automatic cake release or washing. |
| Nettoyage des tissus | Selected cloth, foulant and supplier-approved cleaning method | Wash equipment, water connections, drainage, cleaning access and expected operator work | Identify omitted cleaning equipment or work; obtain a quotation rather than assume an add-on price. |
| Equipment and site supply boundary | Press, feed and conditioning equipment, utility packages, cake handling, support structure, site connections, installation and commissioning | Each item marked included, excluded or optional, with the supplier or buyer responsibility identified | Record added site cost; check the capacity, condition and compatibility of equipment proposed for reuse. |
| Annual operating cost | One operating schedule and trial-supported assumptions | Polymer, electricity, wash water, wear parts, cleaning labor, maintenance and cake-disposal costs | Keep uncertain inputs as explicit alternatives rather than assign unsupported savings. |
| Delivery and commercial commitments | The same performance and delivery boundary | Utilities and installation responsibilities, acceptance basis, lead time, warranty and service exclusions | Keep missing commitments visible before comparing the final commercial total; early budget offers may retain open items. |
The comparison sheet is one table with a row for each requirement and four columns: the common basis you issued, what each supplier included, what they excluded, the evidence behind any performance figure, the site cost you must add, and the decision still unresolved. Built this way, the sheet ranks offers only after the scope gaps have been priced or flagged, which is the opposite of ranking on headline price and discovering the gaps during installation.
Keep automation functions on separate rows. A press offering automatic plate shifting with manual cloth washing and a press offering both are not the same product, and writing them on one “automation” row hides exactly the difference that decides staffing. The same applies to duty rows when the plant has two distinct streams — give each its own group so a supplier strong on one is not credited for the other.
Where an item is missing from a quote, write the exclusion and the work it creates, and leave the price cell empty until the supplier quotes it. Inserting an assumed add-on figure converts a known gap into a false number, and the comparison loses the one thing it was built to preserve: the reason a cheaper offer needs adjustment. Porvoo’s fully automatic filter press offers can be read the same way, function by function, against the same sheet.
Before the bid review, have the duty basis in writing, recent slurry analyses covering normal and off-normal production, the daily dry-solids load and operating hours, the filtrate destination and its quality requirement, the disposal route and cost per tonne for the cake, and a site drawing showing available headroom, floor loading, drainage and the utilities already present. With those in hand, the unresolved column shrinks to the items that genuinely need a supplier answer.
Questions fréquemment posées
Q : Can I shortlist suppliers from budget quotes before slurry testing is complete?
A : Yes, for provisional screening. Compare the stated duty and supply scope while keeping untested output and cake condition open. Before treating a preferred offer as a final bid, agree the representative test feed, complete-cycle basis, measured outputs and acceptance basis needed to resolve those uncertainties.
Q : Our plant has several slurry streams. Should we compare them as one duty?
A : Combine them only when the comparison basis represents their actual requirements. Record each stream’s source, feed solids, variability and required endpoints, then establish which conditions each offer covers. Keep genuinely different duties in separate comparison groups so a favorable result for one stream does not stand in for evidence for another.
Q : Can we count existing feed or cake-handling equipment as a saving?
A : Treat reuse as a conditional saving until its capacity, condition and compatibility with the proposed press and duty are checked. Identify who provides the connections and any necessary changes, then obtain prices for that work. Compare the resulting site total rather than deducting an assumed replacement cost from one supplier’s offer.
Q : What should we do if the cheapest bid changes when operating-cost assumptions change?
A : Keep the ranking conditional and identify the assumption that reverses it. Compare explicit alternatives for uncertain items such as cake-disposal cost, cleaning labor or wash-water use on the same operating schedule. Resolve the decisive uncertainty through the relevant trial evidence or scope clarification before relying on a claimed annual saving.
