Finding the right gate valve
Part 2: Spindle & Seals
How to choose a better gate valve? Part 1 of this guide covered using standards compliance, materials selection, high-quality processing, and design value as indicators of valve quality and ultimately of the gate valve’s long term performance. The final part of this guide expands on those principles as they relate to the spindle and the seals of the gate valve, then delivers a brief summary of all the checks outlined in this guide so far. With this you can quickly assess whether a gate valve will continue to operate long after installation, or will fail prematurely, leading to costly repair work.
Checking the spindle and seals
The spindle, also known as the stem, is the core element for gate valve actuation. Inspecting this component for quality before installation can save you in the long term, because if its threaded surface is damaged, which commonly occurs from corrosion, the spindle can abrade the wedge nut, typically made of softer brass material, making the valve harder to operate. The seals around the spindle and bonnet can also be checked to ensure they will not prematurely fail in service, resulting in water leakage.
Tip 1: Adequate number of seals
- There should be a minimum of 4 seals here, with 2 between the spindle and the spindle bearing or O-ring carrier and another 2 between the carrier and the bonnet. There should also be a wiper ring on top of the bonnet to avoid the ingress of dirt and other foreign material.
- The thickness of the seals must be 3 mm or greater, as thin O-ring seals have less sealing area and will wear out faster.
Tip 2: Easy maintenance
- Confirm that the O-rings or other spindle seals can be replaced while the pipeline is in service. Although not needed very often, this can prevent service interruptions and reduce maintenance costs.
Tip 3: Corrosion protection of the threads
- Verify that the bonnet gasket interlaces with the bolts. A gasket that does not do this will allow corrosion of the threads in the valve body.
Tip 4: Spindle bearing and/or O-ring carrier are reliably fixed in the bonnet
- Threaded connections are the most prone to damage and/or leakage and should be avoided in favor of a bayonet or double bayonet style connection. The double bayonet connection is the best, as it prevents unwanted unturning of the assembly that could result in the possibility of leakage and also spreads the load on the bonnet coating over a larger area.
- For the bayonet style connection, ensure the internal surfaces of the bonnet are completely coated to prevent corrosion.
Tip 5: What makes a gate valve easy to operate?
- Ensure there are sliding disks (or gliding disks) on both sides of the spindle collar. If these are not present the valve becomes extremely difficult to actuate after a few uses.
- If the gate valve is larger than DN 200, confirm the spindle bearing has a ball bearing component. For larger gate valves, ball bearings tend to help maintain easy valve actuation, even after several years in service.
Advanced spindle checks
The following expert spindle checks require additional testing which may or may not be provided by the manufacturer:
Tip 6: Spindle material
- Confirm that the spindle material of the gate valve matches what is claimed by the manufacturer. This can be done using a spectrometer, which provides a break-down of a material’s chemical composition.
- Based on the chemical composition, you can then calculate or look up the pitting resistance equivalent number (PREN), a reliable indicator for through-wall corrosion resistance. As a general rule, if you are unsure about the corrosivity of the water and/or the soil around your valve, you should choose a spindle material with a PREN value of 25 or greater.
The spindles of Hawle E3 gate valves are cold-rolled, also on the shaft, thereby achieving extremely smooth surfaces. This preserves the wedge nut as well as the spindle sealing O-rings.
By following the recommendations listed throughout Part 1 and Part 2 of this guide, you can be confident that your next gate valve will perform better, last longer, and have a lower lifecycle cost than a lower-quality alternative. The Hawle E3 gate valve meets or exceeds all the best practices explored by this guide. Following the below-summarized inspection points will help you to select a top-quality valve that you can depend on:
Only high-quality materials
- Are made of top-quality GJS400-15 ductile iron
- Use lead-free materials
- Use a spindle made of 1.4162 duplex stainless steel, which has a chromium content of 21.5% for extremely high corrosion resistance and reliable long-term strength
- Come with edge protectors against mechanical damages
- Use a wedge guiding system consisting of low-friction, grooved, and plastic-covered nose pieces
- Have a form-fit wedge nut
- Have minimum 4 O-ring spindle seals with a 3 mm thickness or more, which can be replaced while the valve is in service
- Have a bearing and/or O-ring carrier that is reliably fixed to the bonnet with a double bayonet style connection
- Have sliding disks, and/or a ball bearings: No bypass required for larger dimensions
Compliance with the srictest quality tests
- Meet or exceed applicable quality standards for longevity and safe usage with potable water
- Coating with bond strength of at least 18 N/ sq mm
- Stand up to rigorous endurance testing, continuing to perform even after more than 2500 actuation cycles
Manufactured using the latest production techniques
- Are reliably coated, internally and externally, using fluidised bed epoxy coating process
- Are manufactured with strict quality requirements to ensure they are free of casting defects or coating/vulcanization imperfections
- Have machined flange surfaces for improved sealing.
If you are not sure what type of gate valve is appropriate for your application, contact our service team for expert technical consultation.