A polyphosphate retrofit survey is first a dimensional survey. Before anyone can quote a dosing unit, a bypass loop, or a replacement cartridge housing, they need to know whether the device will physically fit into existing pipework and whether the flow through it can be controlled. The dimensions that most often decide the outcome are the true pipe outside diameter and material, the internal bore at the connection point, the exact length of pipe to be cut out, the orientation and flow direction, the free space around the installation, and the clearance needed to extract and replace the cartridge. Flow rate, pressure, temperature, and water chemistry should be recorded in the same visit, because they determine whether a full-flow or partial-flow (bypass) arrangement is appropriate.
This matters to contractors, mechanical engineers, and water-treatment distributors who are being asked to retrofit a slow-dissolving polyphosphate glass — often referred to by the trade name Siliphos or as polyphosphate crystal — into a building that was never designed for it. Siliphos-type media are not all identical, and a cartridge dimension that fits one supplier’s housing will not necessarily fit another’s. The survey should therefore capture data that is independent of any single product.
Why nominal pipe size is not enough
The single most common survey error is recording the nominal size and assuming it identifies the pipe. It does not.
- Steel pipe is specified by nominal bore, but the outside diameter is fixed while the wall thickness changes with schedule. Two DN25 pipes can have measurably different internal bores.
- Copper tube is usually specified by outside diameter, so a “22 mm” tube is 22 mm on the outside regardless of wall thickness.
- Plastic pipe (PEX, PPR, PVC-U, HDPE) is generally specified by outside diameter, but the joining system — compression, push-fit, electrofusion, solvent weld, butt fusion — changes the space and tooling required.
- Imperial and metric systems are frequently mixed in older buildings, and a 1/2 inch designation never means 12.7 mm of anything measurable.
For a retrofit, what the installer actually needs is the measured outside diameter at the point where the fitting will grip, plus the material, plus the joining standard. Take the measurement with a caliper or an outside-diameter tape at the exact location of the proposed connection, not somewhere convenient along the run.
Pipework dimensions to verify on site
The table below is a practical survey checklist. Every row should be recorded with a photo and a sketch, because a dimension without a location is useless to the person designing the assembly.
| What to verify | Why it matters | How to record it |
|---|---|---|
| Pipe outside diameter at the connection point | Determines which clamps, compression fittings, or saddle adapters are available | Caliper or OD tape, in millimetres, with a photo of the tape in place |
| Pipe material and joining system | Determines whether the pipe can be cut, threaded, or must be adapted | Material name, manufacturer marking, and a close-up of the marking |
| Wall thickness or internal bore | Affects velocity, pressure drop, and whether the required flow can pass through the pipe at all | Measured bore at an open end, or wall thickness from the pipe marking |
| Thread, flange, or coupling standard | Prevents ordering a unit that cannot be joined without an adaptor | Identify the standard and size; photograph the exposed thread or flange face |
| Flow direction and pipe orientation | Housings and bypass loops are directional and may need a defined mounting attitude | Arrow on the sketch showing flow, plus horizontal, vertical, or inclined run |
| Cut-out length between the two proposed cut points | The assembly must match the gap it replaces, including fittings and any spool pieces | Measure face-to-face after marking the cut lines, then re-measure |
| Offset and angular misalignment between cut ends | Rigid assemblies will not pull together if the two ends are not coaxial | Vertical offset, horizontal offset, and angle in degrees |
| Centreline height and distance to walls, ceiling, and joists | Determines bracket positions and whether the unit can be mounted at all | Three measurements from fixed references, not from the floor alone |
| Cartridge extraction clearance | A housing that fits may still be unserviceable if the cartridge or bowl cannot be removed | Free distance in the direction of removal, plus clearance for tools and hands |
| Distance to heaters, meters, pumps, softeners, and backflow devices | Injection point placement affects performance and may be constrained by regulation | Measured distance downstream or upstream, with a simple line diagram |
| Isolation valves and drain points | Servicing a cartridge without isolation means shutting down the building supply | Note valve type, condition, and whether a drain is available nearby |
| Pipe support and substrate | Added weight and vibration need suitable anchoring | Wall or floor construction, existing bracket spacing and condition |
Hydraulic and water-condition data to capture in the same visit
Dimensions alone will not tell you how to configure the installation. Record the following while you are on site, because a second visit is far more expensive than a longer first one:
- Flow rate — peak and typical, ideally measured rather than assumed from nominal pipe size.
- Static and dynamic pressure at the proposed injection point.
- Water temperature at the injection point and downstream. The dissolution rate of polyphosphate glass generally increases with temperature, so the supplier needs the actual figure to advise on cartridge selection and orientation.
- Source water analysis — hardness, alkalinity, pH, iron, manganese, chloride, and any other parameter the supplier requests. Existing scale or corrosion history is also useful.
- Existing treatment — softeners, filters, UV units, or dosing pumps already in the line, and whether the polyphosphate device will be upstream or downstream of them.
- Demand profile — continuous or intermittent, since intermittent draw affects how much water actually contacts the medium.
Be clear about what the technology does. Polyphosphate dosing is a scale-inhibiting and film-forming treatment: it interferes with crystal growth and can help control corrosion in some systems. It is not a softener, it does not remove existing scale, it does not filter particles, and it does not disinfect. If the client’s problem is hard water leaving deposits inside a calorifier, or old scale blocking a heat exchanger, the survey should record that distinction before any product is proposed.
Site conditions that are easy to overlook
Serviceability, not just fit
A unit can pass a dimensional check and still fail in service. Ask the maintenance team how often they expect to change cartridges, who will do it, and what equipment they will bring. A housing mounted high on a wall with no platform may be technically compliant and practically unusable.
Metallic pipe continuity
Cutting a metallic pipe can interrupt electrical continuity bonding. Before cutting, identify whether the pipe is being used as a bonding path and confirm who will restore it. This is a safety item, not a preference.
Regulatory position for drinking water
Food-grade material and drinking-water approval are not the same thing. Suitability for potable water depends on the exact product, the dose achieved, the contact material, and the rules of the destination market. Where potable water is involved, confirm with the supplier and the local authority which documentation is required before installation, and do not treat a general product description as evidence of approval.
Backflow and cross-connection
Any device that introduces a medium into a supply line may require backflow protection. Confirm the requirement for the specific building and jurisdiction during the survey so it can be included in the quotation rather than added later.
What to do when a dimension cannot be verified
Do not substitute a plausible value. If a pipe is buried, insulated, or inaccessible, record it as unverified and state what has to happen next — for example, a small inspection opening, a temporary shutdown, or a thermographic or ultrasonic check. A quotation built on assumed dimensions transfers the risk of a rework to the installer, and rework in occupied buildings is expensive.
The same applies to water chemistry. If no recent analysis exists, the honest position is that the analysis is outstanding, not that the water is “probably hard”.
Frequently asked questions
Can I size a polyphosphate unit from the pipe diameter alone?
No. Diameter determines the connection, but unit sizing depends on flow rate, the fraction of flow that should pass through the medium, contact time, and the manufacturer’s own configuration guidance. Diameter is a fit question; flow is a performance question.
Should the unit be installed full-flow or in a bypass?
That depends on the product and the treatment objective. Many polyphosphate installations use a controlled partial flow so that only a portion of the water contacts the medium, which allows the dissolution rate to be managed. The correct configuration must come from the product supplier, based on the flow data you collect. Do not decide it on site by eye.
How much clearance should I allow for cartridge replacement?
Allow the full removal distance stated by the equipment supplier, plus working space for hands and tools. If that figure is not available yet, record the free space you actually have and let the supplier confirm whether it is sufficient.
Do I need isolation valves if the existing line has none?
If the cartridge or housing requires periodic replacement, the practical answer is almost always yes. Record the current valve arrangement so the scope of the retrofit is clear.
Recording the survey so it can be quoted
A useful survey pack contains a marked-up sketch of the pipe run, photographs with a scale in frame, the measured outside diameter and material at each connection point, the cut-out length and offsets, clearance figures in the direction of cartridge removal, and the hydraulic and water-quality data listed above. With that pack, a supplier can confirm fit and configuration without a return visit.
If you are planning a polyphosphate or Siliphos-type retrofit and need help matching a cartridge format to your measured pipework, send ENVO CHEMICAL the application (potable or process water, and the treatment objective), the pipe material, measured outside diameter and connection standard at the injection point, cut-out length and available clearance, plus flow rate, pressure, temperature, and any recent water analysis. That is the minimum needed to give you a specific answer rather than a generic one.
