Engineering playbook
Inflatable Pipe Plug Sizing and Back-Pressure Playbook
Convert water head to pressure, shortlist published inflatable plug models by pipe bore, and check back-pressure limits before an isolation or testing job.
Who is this field playbook for?
Use the published model data to convert static water head into pressure, shortlist inflatable plugs that cover the measured pipe bore, and see which models list a back-pressure limit at or above the calculated head. The result is a screening check, not a project approval.
Calculate the field result
Change the inputs to match the job. The result updates immediately and is not stored or submitted.
Pipe plug back-pressure and water-head calculator
Convert a static water head to pressure at the plug, then compare it with the maximum back pressure published for each model. Use the upstream water level above the plug, not the pipe diameter.
Static pressure: 0.49 bar · 7.1 psi
11 published models cover DN300; 11 list a back-pressure limit at or above this static head.
| Product | Model | Pipe range | Max back pressure | Check |
|---|---|---|---|---|
| Test plug | TP-DN300 | DN300–300 | 5.0 bar | Rated for this head |
| Test plug | TP-DN300 | DN300–300 | 3.0 bar | Rated for this head |
| Multi-size plug | HMSP 200-400 | DN200–400 | 2.5 bar | Rated for this head |
| Multi-size plug | HMSP 300-600 | DN300–600 | 2.5 bar | Rated for this head |
| Multi-size plug | MS 150-300 | DN150–300 | 1.0 bar | Rated for this head |
| Multi-size plug | MS 200-400 | DN200–400 | 1.0 bar | Rated for this head |
| Multi-size plug | MS 200-500 | DN200–500 | 1.0 bar | Rated for this head |
| Multi-size plug | MSBP 200-300 | DN200–300 | 1.0 bar | Rated for this head |
| Multi-size plug | MSBP 300-500 | DN300–500 | 1.0 bar | Rated for this head |
| Single-size plug | SS 300 | DN300–300 | 1.0 bar | Rated for this head |
| Multi-size plug | MS 300-600 | DN300–600 | 0.5 bar | Rated for this head |
Static head only. Add the project allowance for surge, flow, pipe condition and temperature, and confirm the selected model, accessory arrangement and test procedure with Reliance. A catalogue back-pressure figure is not a project approval.
How to use the back-pressure result
- 1
Use the upstream water level
Measure the static water level above the plug, not the pipe diameter. Convert it to pressure, then compare that figure with the published maximum back pressure for the selected model.
- 2
Check the bore and the access
The published model range must cover the measured internal diameter. Also check the deflated dimensions, inflation equipment and the route into the pipe before the plug is sent to site.
- 3
Add the project allowance
The calculator shows static head only. Surge, flow, temperature, pipe condition and the test procedure can raise the load. Confirm the final arrangement, accessory set and permitted pressure with Reliance.
Static head is not the whole load
A plug holding back a static column sees the head above it. A flowing sewer, a pressure test or a sudden release can add surge and dynamic loads. The published back-pressure limit is a model reference, not a permit to work. Use the site risk assessment and the responsible engineer's procedure for the isolation.
Multi-size, single-size and testing plugs have different published limits. Do not copy a figure from one table to another model.
Frequently asked questions
How is water head converted to pressure at a pipe plug?
One metre of static water head produces about 0.098 bar, or 1.42 psi. Multiply the upstream water level above the plug by that factor. Use the water level, not the pipe diameter, and add the project allowance for surge, flow and temperature before comparing the result with a published back-pressure limit.
What is the difference between inflation pressure and back pressure?
Inflation pressure is the air pressure inside the plug that expands it against the pipe wall. Back pressure is the pressure from the pipe contents acting on the plugged section. They are separate published limits. A higher inflation figure does not establish a higher permitted back pressure, so read the row for the selected model and confirm the accessory arrangement.
Does the calculator select the final plug model?
No. It shortlists models whose published bore range covers the measured diameter and whose published back-pressure figure covers the calculated static head. The final selection still needs the actual internal diameter, ovality, pipe condition, access, deflated dimensions, inflation equipment, confined-space procedure and project safety review.
Published data and sources
Need the job checked?
Send the measured bore, pipe material, water head or access opening, selected model and destination. Reliance will confirm the available configuration and the documents needed for the order.
Send a technical enquiry