Firefighting Water Reserve
Useful as a receiving or temporary supply point during water shuttle operations. Specify hose couplings, access clearance, refill cycle and site-approved operating procedures.
Portable Liquid Containment / OEM Supply
Onion Tanks for Rapid-Deployment Water Storage
Self-supporting, collapsible open-top water tanks for firefighting reserve, emergency water staging, irrigation and temporary field supply. DERFLEX can match reinforced PVC or project-selected TPU coated fabric, floating collar, outlet fittings, tank dimensions and OEM packaging to the way your team actually deploys and drains water.
Open-top / optional coverSelf-rising collarCompact when emptyCustom valves & connections
DERFLEX product archiveField-ready flexible tank formatsAuthentic DERFLEX photo: red onion-style tank (left), closed pillow tank (right). The two designs serve different filling and containment needs.
Self-supportingWater-filled open tank without a rigid external frame
Weldable textilePVC coated polyester; TPU direction by project review
Custom connectionsOutlet, drain, coupling, collar and ground protection
OEM / bulk supplyProject drawings, branding, packing and accessories
The Product, Clearly Explained
What is an onion tank?
An onion tank is a collapsible, self-supporting liquid-storage tank with a broad circular base, sloping flexible sidewalls and a large open top. A buoyant collar helps the opening rise as the tank fills, allowing temporary storage without installing a rigid external frame.
Also called an onion water tank, self-rising tank or self-supporting firefighting water tank, this format is useful where fast top filling, visual access and compact empty-state transport matter. An optional cover can reduce debris ingress, but an open-top tank should not automatically be treated as hygienically sealed.
For the wider product family—including closed bladders and frame-supported options—see DERFLEX's flexible water tank manufacturing overview.
Buyer Decision
Choose an onion tank when the operation needs...
- Fast field placement with minimal assembly and open top access.
- A receiving or shuttle reservoir for pumps and hoses.
- Folded storage between seasonal or emergency deployments.
- Project-specific outlet / drain position and connection sizing.
- A material and seam design evaluated for the liquid, climate and use cycle.
01 / Technical Selection
Onion Tank Specifications That Actually Matter
Capacity alone cannot describe a field tank. The purchase specification should define the filled footprint, operating liquid, water-access method, structural fabric, collar geometry, connections and the intended deployment cycle.
| Specification | DERFLEX sourcing direction | What to confirm before ordering |
|---|---|---|
| Tank type | Open-top, self-supporting onion-shaped flexible tank; optional cover subject to design. | Open access vs contamination control; top opening and collar dimensions. |
| Capacity | Project-sized; existing DERFLEX flexible-tank family references cover approx. 500–500,000 L, not an onion-specific guaranteed range. | Required usable liters or US gallons; fill height, footprint and stability review for this particular onion design. |
| Coated fabric | Reinforced PVC coated polyester; selected TPU coated fabric alternatives can be reviewed. | Stored liquid, UV exposure, folding cycle, service temperature, chemical or potable-water requirements. |
| Weight / thickness | Specified by project. Existing DERFLEX flexible-tank directions include approx. 0.75–1.20 mm for selected products, with other grades possible. | Approved TDS, tensile / tear strength, coated-fabric adhesion, weld trials and target performance. |
| Floating collar | Self-rising collar concept; buoyancy, collar material and optional hose support to be agreed. | Opening diameter, collar construction, fill-hose loading and folding method. |
| Seams & edges | Compatible HF / RF or thermal welding route, reinforced high-stress areas where needed. | Panel layout, seam validation, base transitions, fitting reinforcement and workmanship checks. |
| Outlet / drain | Custom valve, adapter, coupling and discharge positioning available for review. | Thread / camlock standard, nominal bore, pump suction, discharge rate, hose restraint and closure. |
| Color / accessories | Project color, printed mark, groundsheet, cover, storage bag and repair accessories by agreed scope. | Color sample, print location, packing method, spare fittings and field repair plan. |
| Production & commercial | OEM / wholesale / engineered projects; samples and order terms discussed after review. | Quantity, drawing, destination, required documents, sample plan and target schedule. |
Specifications are a procurement framework, not a certified datasheet for a stock model. Do not apply material references from other tank geometries as automatic performance guarantees for a finished onion tank. For related fabric and system design, see heavy-duty tarpaulin tank engineering considerations.
02 / Original Product Imagery
Coated-Fabric Water Containment in Real Applications
Authentic images from DERFLEX's existing website show how flexible tank formats differ. The onion tank is the primary subject of this page; adjacent formats below are for technical comparison, not mislabeled as onion tanks.
Image Comparison
Do not confuse open access with identical structure.
Open-top containment may use a floating rim, a rigid support frame or another support mechanism. Procurement documents must state exactly which design is required.
DERFLEX product photography · comparative tank type
All images above are hosted on derflex.com. Historical photographs may carry original brand watermarks; finished product details should be confirmed with the current quotation and approved sample.
03 / Application-First Selection
Specify the Tank Around the Mission
Instead of treating “heavy duty” as a single fabric grade, decide which parts of the operation place the greatest demand on the finished tank.
Fire-response staging
Prioritize fill & discharge
State water shuttle volume, the pump or tanker connection, target fill rate, outlet size and crew access around the rim. Review hose restraint and emergency drain procedure.
Repeated field use
Prioritize flexing & repairs
Define expected folding frequency, abrasive ground conditions, protective sheet, seam design and the spare fitting / field repair policy before selecting coated fabric.
Remote irrigation
Prioritize outdoor exposure
Review UV, soil or gravel substrate, seasonal storage, outlet elevation and the required flow to irrigation equipment. Confirm cover needs for debris control.
Sensitive water use
Prioritize contact compliance
Define water purpose, contact duration, destination-market requirements and cleaning plan. A general-purpose open PVC tank is not automatically drinking-water approved.
04 / Fabrication Engineering
Where an Onion Tank Gains or Loses Reliability
The self-supporting geometry changes with the water level. Tank behavior depends on more than material thickness: the collar, seam transitions, outlet load and ground contact must work together.
01
Define filled geometry
Agree target volume, opening diameter, base footprint, maximum working height and clearance before pattern making.
02
Select coated fabric
Review PVC / TPU chemistry, reinforcement, flex performance and approved welding parameters for the actual liquid.
03
Design the collar
Specify buoyancy, protective finish, top access and the effect of filling hose position on the floating rim.
04
Reinforce fittings
Match discharge interface, patch geometry and hose restraint to expected hydraulic and handling loads.
05
Inspect as a system
Agree dimensions, weld appearance, fitting integrity, tank leak check and traceable approval criteria.
For a polyurethane-coated material route and welding considerations, review DERFLEX TPU flexible water tank fabric. The selected construction must be qualified for the planned use.
05 / Format Comparison
Onion Tank vs Pillow Tank vs Frame Tank
The correct tank style follows the water-handling workflow. If an operation requires frequent open access, a closed bladder is not a direct substitute. If clean enclosed storage is essential, an open onion tank may be the wrong default.
| Decision point | Onion / self-supporting | Pillow / closed bladder | Frame-supported tank |
|---|---|---|---|
| Top access | Large open top; optional cover subject to design | Sealed; access through designated ports | Open top commonly available |
| Field setup | Deploy on prepared ground; self-rises with filling | Unfold and connect filling / venting lines | Install or verify frame + liner first |
| Containment priority | Fast receiving, inspection and water transfer | Enclosed temporary storage | Stable open tank geometry / process access |
| Empty-state logistics | Collapsible; collar influences pack size | Collapsible and compact | Liner folds; frame ships separately |
| Key buyer risk | Spillage, debris, flotation rim / hose loads | Valve / seam issues and inaccessible interior | Frame stability, liner abrasion and setup time |
06 / Real-World Applications
Where Self-Supporting Onion Tanks Fit
These applications share a need for portable water capacity, but they should not share an unexamined material specification. Access, storage duration, water quality and field hazards change the purchasing decision.
Disaster & Relief Staging
Compact transport supports field deployment when utilities are disrupted. Confirm intended water quality, hygienic precautions, handling personnel and local response requirements.
Irrigation & Farm Reserve
Temporary water buffers for seasonal irrigation and remote field work. Review soil preparation, outdoor exposure and outlet interface; also see agricultural water storage designs.
Jobsite Utility Water
Portable supply for washing, site maintenance and selected dust-control operations. Keep equipment traffic away from the filled tank and protect the base from debris.
Remote Water Transfer
Interim receiving capacity between tanker, pump and point of use. Define available pumping head, inlet placement, drain speed and isolation of the work area.
Temporary Process Water
Suitable only when the actual water chemistry, temperature, cleaning method and any containment obligations are checked. Do not assume chemical compatibility.
07 / Before You Deploy
What Buyers Should Know Before Filling an Onion Tank
These practical requirements should be part of field instructions and procurement review—not discovered after the tank arrives on site.
Critical deployment considerations
- Surface: Use a stable, suitably level site; remove sharp debris and add ground protection where needed. Confirm allowable slope for the exact design—do not borrow another manufacturer's published slope rating.
- Water load: 1,000 liters of water weighs approximately one metric tonne. Confirm subgrade bearing conditions and safe access before filling.
- Open top: Control debris, splash, insects, evaporation and overflow. Use an appropriate cover when the application calls for one.
- Fittings: Restrain hoses so pumps and pipework do not pull on the outlet fitting. Position suction to avoid drawing fabric into the intake.
- Liquid approval: Potable water, fuels, wastewater and chemicals require different checks. Never infer suitability from a generic PVC or TPU label.
- After use: Drain safely, clean and dry as required, inspect seams / collar / fittings, then fold and store under the approved procedure.
Load Awareness1,000 L
≈ 1 metric tonne of water
Water volume translates into substantial ground load. Tank volume, actual filled dimensions and ground condition must be reviewed together.
Practical Planning Aid
Estimate filling time and water mass
Enter the planned liters and sustained fill rate. This simple estimate excludes hose, pump and site losses; it does not calculate tank dimensions or validate site stability.
Illustration: 10,000 L weighs about 10 metric tonnes and fills in approximately 20 minutes at a sustained 500 L/min.
08 / Wholesale & OEM Projects
Send a Drawing. Receive a More Relevant Tank Proposal.
A complete RFQ helps determine whether a self-supporting open-top onion tank is the correct form and which material, fittings, footprint and accessories should be evaluated. DERFLEX can discuss color, marking, packaging, repeat-order scope and material-to-fabrication details.
Request a Custom Quote01 Target usable capacity
02 Stored liquid & compliance
03 Site diameter / slope / ground
04 Fill & discharge rate
05 Connection type & size
06 Exposure & operating cycle
07 Collar, cover & accessories
08 Quantity & destination
09 Branding / packing / sample
10 Drawing or reference photo
No fake online price, minimum order quantity or delivery promise: terms are confirmed against the approved project specification.
09 / Buyers Ask
Onion Tank FAQs
Direct answers for engineers, emergency water planners, distributors and international procurement teams.
What is the difference between an onion tank and a pillow tank?
An onion tank is generally an open-top, self-supporting field reservoir that rises as water is added. A pillow tank is a closed flexible bladder that expands during filling. Onion tanks favor rapid top access; pillow tanks favor enclosed storage.
Does an onion tank need a metal frame or air inflation?
A self-supporting onion design does not normally require an external metal support frame. Its buoyant collar helps keep the top opening raised as it fills. Specific collar construction varies; confirm whether the selected version uses foam, an air-filled element or another approved arrangement.
Can DERFLEX customize onion tank capacity and fittings?
DERFLEX supports project-based flexible tank sizing, coated-fabric selection, valve and connection layouts, color, branding and accessories. Exact onion tank capacity, footprint, dimensions and operating limits require engineering review before confirmation.
What material is used for a collapsible onion water tank?
Reinforced PVC coated polyester is a common construction for collapsible water tanks. TPU coated technical fabric can also be reviewed when folding behavior, liquid-contact requirements or operating conditions call for a different material. Material names alone do not establish final suitability.
Are onion tanks suitable for potable drinking water?
Not automatically. Drinking-water suitability depends on the exact liquid-contact materials, the finished assembly, required destination-market standards, cleaning practices and verified supporting documentation. Request a project-specific compliance review before specifying potable-water use.
How should an onion tank be placed on the ground?
Choose a stable, level, clean area that can support the fully filled water load. Remove stones, sharp debris and exposed edges, and use a protective groundsheet where necessary. Permitted slope and filled footprint must be confirmed for the specific tank model.
Can an onion tank store chemicals, fuel or wastewater?
Only after reviewing the exact liquid composition, concentration, temperature, contact time, cleaning chemicals and secondary-containment requirements. A standard water-storage tank should not be assumed compatible with fuels or industrial chemicals.
What information is required for an onion tank wholesale quotation?
Provide target usable capacity, intended liquid, installation surface, available footprint, fill and drain rates, hose / valve connection standard, deployment frequency, operating climate, accessories, quantity, destination and any OEM documentation.