Concrete pumping manual shut off valve failure

Issued: 14/05/2024
Last Updated: 16/05/2024

Purpose

The purpose of this safety alert is to provide guidance on hazards associated with concrete pumping manual shut off valves, and to provide guidance on markings and information that should be provided by manufacturers, importers, suppliers and concrete pumping employers.

Manual shut off valves are also known as hammer shut off valves or slide valves. An example of a manual shut off valve is shown in Figure 1.

Background

In late 2023 there was an incident in Brisbane where six bolts on a slide valve broke causing pressurised concrete to be released from the concrete pump line (refer Figure 2). The bolts are believed to have been M16 bolts. The combined capacity of six bolts of this size is significant so the concrete pressure at the time of the incident was likely high. No injuries occurred but the incident had the potential to cause serious injuries due to the high pressure of the escaping concrete.

Manual shut-off valves are typically supplied for use on bottom filled formwork, enabling the use of multiple filling ports to prevent concrete flowing out of the form when switching ports or when pouring is interrupted or completed. They may also be used on fixed vertical concrete pumping lines to prevent air pockets in the line when the pump is paused during pumping.

Manual shut-off valves are opened and closed by hitting the valve plate sideways with a hammer. The valve plate slides between the two flat side plates and is provided with a circular hole that matches the pipe internal diameter when fully open. The valve plate is slightly thinner than the spacer bars, one of which is provided on each side of the sliding plate.

Unlike other parts of concrete pump lines such as clamps, bends and pipelines, very little guidance on the marking, use and maintenance of manual shut off valves is available.

_{Figure 1 - One type of manual shut off valve}

_{Figure 2 - Two halves of valve have separated due to bolt failure}

Contributing factors

The cause of this incident is unknown; however, failures of this type of valve can occur due to one or a combination of the following:

• Bolt failure due to concrete pressure being applied by the pump that exceeds the bolt strength, with the valve either partially or completely closed.
• Bolt failure due to damaged, corroded or fatigued bolts or due to the incorrect grade of bolts being used (note: using bolts of a higher tensile grade does not necessarily make the valve more robust – higher grade bolts can be more prone to cracking, especially if incorrectly tightened).
• Bolt failure due to under or over tightening.
• Excessive wear on the pipe wall of the valve assembly and rupture of the pipe (i.e. the wall thickness reduces to the extent that the pipe bursts).
• Failure of the welds on the pipe flanges or between the pipe and flat plate – due to cracking or inadequate weld size and/or penetration.

Unfortunately, the maximum permissible operating pressure of manual shut off valves is often less than the maximum possible concrete pressure that a pump can apply. This is especially the situation on pumps used on high rise jobs, where the pump needs to be capable of pumping concrete at very high pressures. If a blockage occurs and the pump operator applies maximum pressure to the system with the valve closed, the valve can blow apart – this is especially a risk at early stages of the job where the end of the concrete line and the location of the manual shut off valve are relatively close to the pump where pressures are highest.

It is important that concrete pump pressure does not exceed the maximum pressure rating of the component with the lowest pressure rating in the pumping line. This must also factor in reduced pressure rating of components as they wear.

Manual shut off valves can also be damaged from high forces applied when the slide plate is opened and closed with a hammer.

Action required

Manufacturers, importers, and suppliers of manual shut off valves

The Work Health and Safety Act and Regulation 2011 set out duties for manufacturers, importers, and suppliers of plant. To help demonstrate compliance with the duties imposed by the Act and Regulation the following should be carried out:

Documented user instructions provided to the end user that include:

1. The maximum permissible concrete pumping pressure that the valve can safely withstand with the valve closed (including appropriate factors of safety).
2. Bolting details including bolt size, grade, material/surface treatment, and tightening torque and sequence.
3. Inspection instructions including inspection intervals and discard criteria (e.g. how often do bolts need to be removed and examined, what is the minimum pipe wall thickness, what parts need to be inspected, what is the valve plate and spacer tolerance for discard?, etc).
4. Repair procedures, where this is permitted by the manufacturer, including material specifications and welding specifications and instructions.

Manual shut off valves should be permanently marked with the following information:

• The manufacturer’s name or trademark.
• The maximum permissible concrete pumping pressure that the valve can safely withstand when the valve is closed.
• The model numbers.
• A batch number (this may reduce the number of units that may need to be returned if a product recall occurs).

Persons in control of concrete pumping operations

Adequate information is to be provided to workers who install, use, and maintain manual shut off valves. This includes providing the manufacturer’s instructions to workers and training workers in the safe installation, use and maintenance of manual shut off valves. This training should include:

• How to open and close the valve without applying excessive force.
• The closing and opening sequence to be applied, that includes closing the valves when the pump is not applying pressure to the pipeline.
• Special precautions to be taken where the pump’s maximum possible operating pressure exceeds the pressure rating of the valve.
• How to limit the concrete pumping pressure of the concrete pump when this needs to be done for different jobs and/or phases of construction (e.g. high pressure pumps can be run at a lower concrete pressure for all or much of a job).
• How to inspect and maintain the valve in accordance with the manufacturer’s instructions.
• How to ensure air does not enter the concrete pumping line (e.g. due to incorrect operation of the valve).
• Safe clearing of concrete pipeline blockages.

The person with control of the concrete pumping pipeline, including the manual shut off valve, also has a duty to ensure the equipment is used in accordance with the manufacturer’s instructions and is inspected both before and during use to confirm that it is safe.