Horizontal vs Vertical Leaf Filter: How to Choose

The short answer

Choose the tank by how the cake must leave the filter and by the room your plant has. A horizontal leaf filter takes more floor and much less height, and its leaves can be exposed for access. A vertical leaf filter takes less floor and much more height. We make both, so read this with that in mind.

Do not choose the tank to keep the cake on the leaf. Both tanks normally hold vertical leaves, so in our reading a horizontal tank gives no cake-retention advantage over a vertical one. The patents we found that credit retention to horizontal surfaces are describing a third machine, the horizontal plate filter.

"Horizontal" names the tank. The leaf is a separate question

A leaf filter is a pressure filter: flat elements inside a closed vessel, with solids building up as a cake on the leaf surface while clear liquid passes through and leaves by a manifold. Two separate things can be horizontal or vertical. A patent on leaf filter cloths puts it plainly: the vessel axis can be "either vertical or horizontal", and the elements can be assembled "with their surface either horizontal or vertical" (US 4,022,695).

Three machines come up in this comparison. Rotary leaf designs are outside this article.

• Vertical tank, vertical leaves. The usual vertical leaf filter.

• Horizontal tank, vertical leaves. The usual horizontal leaf filter. Solid Liquid Filtration Consultants (SLFC) describes "vertically positioned filter leaves" in "a horizontal cylindrical tank" (Mining Technology), and US 4,022,695 says of a horizontal vessel that "the leaves are vertically mounted".

• Vertical tank, horizontal plates. The horizontal plate filter, a stack of plates in an upright shell (US 3,319,794).

The naming is loose enough to mislead. Parker's Twin Filter brochure heads its range "Vertical Leaf Filters", described as vertical leaves "positioned in a horizontal or vertical filter tank" (Parker Twin Filter), while a Making.com listing for Parker's horizontal range says "horizontally positioned filter leaves". Yuwei's guides disagree with each other in the same way: one says a horizontal leaf filter has leaves "mounted horizontally along a central shaft", and another says "only the shell is horizontal". Leaf direction can differ inside a horizontal tank too: STS Canada notes the leaves may sit along the tank axis or across it (STS Canada).

Before comparing two quotations, ask each supplier, us included, for two facts: the tank axis and the leaf plane.

What the leaf plane affects: cake retention

US 4,022,695 says cake has "a natural tendency to fall off either a vertical surface or the underside of a horizontal one", which helps at discharge but brings "the danger of cake falling off at a premature stage, notably when operation is interrupted for any reason". Our reading is that this varies with the cake: US 3,970,564 describes a cake dried by air or gas that breaks off when the elements are vibrated.

Three more patents describe the consequence. They concern plates and filter elements, not leaf filters as such, and each is arguing for its own design, so read them as interested parties:

• US 3,319,794, for a horizontal plate filter, says a few minutes of power failure can mean "a long shut down" with vertical plate filters, "due to the necessity of recoating them and also possibly removing the fallen filter cake". It says its own class can have the flow stopped "without rendering the filter inoperative".

• US 6,113,778, discussing dry cake discharge, says horizontal plates allow vessel pressure to be reduced "without danger of filter cake falling from the surface of the filter plate".

• US 3,970,564 says the cake "does not adhere well to the vertical surface of the filter elements", which it says rules out filling the shell with a cake-washing liquid. Its own remedy is inclined elements.

None of them gives a rate. We found no published figure for how often a cake detaches, or at what pressure.

Our reading is that this exposure comes with the vertical leaf, so a horizontal tank with vertical leaves does not escape it. Yuwei, which sells leaf filters and horizontal plate filters, has already published the same view and rates both leaf layouts "Moderate to low" for cake stability during pauses. One maker's product page points the other way: Hanke calls its vertical layout suitable where "interrupted flow is expected" (Hanke), without saying how the cake is held. If your process stops often, or the cake needs a thorough wash, put the question to the supplier directly and ask how the precoat is restored after a stop.

If cake retention is the deciding requirement, look at horizontal plate designs as well. They have a cost: US 4,022,695 says such a leaf "filters only through its upper surface, which means that half the surface is wasted". That is a different comparison from the one in this article.

What the tank decides

Floor and height

Parker says the vertical layout requires "little floor space", and Hanke says the horizontal "takes a larger footprint". The size of the difference is less often stated, so we worked it out from Hanke's two published tables, the only same-maker, same-area set we found:

• 25 m² of filter area: horizontal 6.9 m² of floor and 2.0 m high; vertical 5.9 m² and 4.1 m high.

• 60 m² of filter area: horizontal 12.6 m² of floor and 2.4 m high; vertical 7.3 m² and 5.2 m high.

These figures are computed from one maker's catalogue, so treat them as a sense of proportion. Hanke's vertical table gives one shell size for several models, so the floor saving moves in steps and shows no steady trend: about 15 to 40 percent across most rows, and the two rows above are the low and high ends of that spread. The exception is 12.5 m², where a smaller vertical shell gives about 65 percent. We left out the 50 m² row, whose vertical floor figure is misprinted. The vertical unit stands about twice as tall between 15 and 60 m². The tables compare equal filter area, not equal cake volume: the horizontal rows use wider leaf spacing, which lengthens the tank.

Three allowances sit outside those numbers. The tables do not say whether the horizontal floor figure includes the length a retracting shell travels, what clearance is needed above a vertical unit to open it, or whether either height includes what sits under the filter to receive the cake. Check all three on the general arrangement drawing. In an existing building, check headroom first.

Maximum filter area

Horizontal tanks reach further. Parker gives up to 120 m² for its vertical layout and up to 200 m² for its horizontal one, and Hanke's pages run to 200 m² horizontal against about 100 to 125 m² vertical. Micronics says the horizontal layout "increases the possible filtration area" (Micronics). In those two makers' ranges, both layouts are available below roughly 100 m², so area alone does not choose for you.

Access to the leaves

In our reading this is the horizontal layout's clearest advantage. Parker's horizontal tank is retractable, "leaving the leaves exposed", so "the filter leaves can be accessed during cake discharge". SLFC builds two arrangements: one keeps the connections on a fixed cover so they need no dismantling when the tank retracts, and the other draws the whole leaf pack out. Envirogen says the layout allows visual inspection of the leaves, and Kaskad visual cake inspection after every discharge.

The vertical layout's case is simplicity. Our reading is that the vertical layout is mechanically simpler: Hanke lists a hydraulic power pack for shell or bundle retraction on its horizontal unit, and lists none on its vertical unit.

How the cake leaves

Parker and Hanke list wet and dry discharge for both layouts. The route differs:

• Vertical, dry: a pneumatic vibrator shakes the leaves and the cake drops through a conical bottom and butterfly valve, so it leaves through a defined outlet.

• Horizontal, dry: the tank or leaf bundle retracts and the cake drops from the exposed leaves, with a pneumatic vibrator to help it. Parker and Hanke list one; some makers offer it as an option. Our reading is that you then need a hopper or conveyor under the full length of the leaf pack.

• Either, wet: spray nozzles sluice the cake off as a slurry. Hanke suggests wet discharge where the cake is too thin to discharge dry or needs to travel by pump.

Hanke suggests dry discharge where the cake is recycled or disposed of as a solid. Whichever route you use, plan for the vessel being out of filtration while it happens. Our cake discharge article covers the downtime side.

Cake capacity may follow leaf spacing

It is tempting to read Hanke's tables as proof that horizontal filters hold more cake. Its horizontal range works out at 30 dm³ of cake per m² of filter area, and its vertical range at about 22. That is a little over a third more.

The same tables offer a possible reason. The horizontal range uses 100 mm leaf spacing and the vertical range 70 to 75 mm, which is a third to over two fifths more. Hanke's vertical page gives available spacing as 30 to 100 mm, and US 4,022,695, writing of a horizontal vessel, says the gap is "usually chosen to suit the cake thickness for a particular duty".

Our reading: the spacing chosen is the likelier cause. The tables cannot prove it, because every horizontal row is at 100 mm and no vertical row is. Nor does the vertical table settle it: its 70 mm and 75 mm rows both work out at about 22. If your solids load calls for a thick cake, specify the cake volume you need and ask for the leaf spacing that delivers it, in either tank. Wider spacing means fewer leaves in a vessel of the same length, so it costs filter area. For the feed mode, see precoat or body feed.

Duty habits are only habits

STS Canada says leaves are mostly fitted in vertical vessels in fine chemicals and in horizontal vessels in heavier process industries, and that vertical units are often applied to polishing slurries with very low solids. Other sources do not line up neatly with it: Parker calls leaf filters typically suitable for fluids with high solids content, across both tanks. Use the habit as a starting point and let the checks below decide.

How to choose, in order

Our suggested order:

1. Fix the machine type. If the cake must survive stops or a full wash, assess a horizontal plate filter before going further.

2. Measure the room. Record floor, headroom and lifting clearance, then rule out whichever tank does not fit, including shell travel and cover opening.

3. Size the area. Well above 100 m² points to a horizontal tank or to more than one unit.

4. Decide how the cake leaves. Wet or dry, into what, and how often.

5. Weigh access. Leaves that must be inspected after discharge favour a horizontal tank.

6. Set the leaf spacing. Work from the cake volume per batch and treat it as a separate decision from the tank.

If two tanks still pass, take the one with less to maintain for your duty.

What we build

We build horizontal and vertical leaf filters. We have built in SS316L, Hastelloy and titanium. Hydraulic open and close is available on the horizontal configuration. Shell retraction and a pneumatic vibrator are arrangements we provide where the duty calls for them, and they are not standard scope. The range we build for horizontal units is 1.5 to 250 m². A discharge cycle typically costs zero to one hour of downtime, depending on the process conditions.

Across all applications, about 1,000 units are installed worldwide across 460+ installations.

Send us your duty

The most useful enquiry gives us the liquid and its temperature, the solids content, whether the cake is wanted wet or dry, how often the process stops, and the floor and headroom you have. We will tell you whether a horizontal or vertical leaf filter fits, and say so if neither does. Contact our engineers.