Slurries are some of the most difficult fluids to pump - from abrasive bitumen to the solid or acid and flammable solutions found in chemical plants, or the mixtures in agricultural processing that are prone to scaling, slurries are thick, filled with solids, and often very abrasive. Choosing the correct slurry valve is crucial as they start, stop, and control a range of slurry compositions.
By choosing the correct slurry valve for your application, you're able to reduce downtime and maintenance costs, while enjoying increased production. On the flip side, selecting the wrong slurry valve can lead to increased downtime, maintenance costs and even reduced production. It's not an exaggeration to state that valve selection can either make or break a plant's production goals. Here are five things to look for when choosing a slurry valve:
1. Valve size and type
The first thing to look for is that you choose the right valve type for the application. Every valve needs to perform a basic function which may include:
- Shut off flow
- Divert flow
- Mix flow
- Pressure relief
- Backflow prevention
- Adjust flow
Knowing the function allows you to decide on the correct valve type. The most common valve types include:
- Check valves
- Ball valves
- Needle valves
- Metering valves
- Toggle valves
- Stopcocks
- Relief valves
- Regulators
- Pinch valves
For instance, low pressure slurries with low temperature require pinch valves. Valves become more specialized for slurries with high temperatures and pressure. Most standard valve designs will not be effective with most slurries, especially abrasive ones, which can cause significant wear on equipment.
Once you've selected the valve type required according to the function required, you need to make sure that you properly size the valve - matching size to expected flow through the system.
2. Materials of construction
Given the fact that slurries are usually corrosive and abrasive, it's crucial that you select the right materials of construction. Viscous or abrasive slurry can lead to scaling or crystallization with the potential to hinder production and damage equipment.
Corrosivity needs to be taken into account, not only for selecting the right sleeve or seat material, but also when selecting compatible material for the valve's body, housing, or gate.
The valve materials must be compatible with the gases or liquids flowing through it, while gates and seats must be made of materials that can withstand the process conditions (for example, natural rubber is best for seat material when slurries are abrasive). Plastic valves usually resist harsh or corrosive chemicals better than metal valves.
3. Pressure and temperature
Determine the pressure and temperature requirements of the plant where the valve will be installed, before choosing your slurry valve. The pressure and temperature of the slurry will determine which materials can be used in your process.
For instance, metal valves tend to withstand higher temperatures and pressures than plastic valves. Metal valves are also usually best for pressurized gases. This is because they tend to be stronger than plastic valves.
4. Specific requirements
Certain valves, such as check valves, have special requirements. Make sure that the chosen valve will work as expected. Look at the response time required as well as cracking pressure to open the valve.
Another consideration is the valve's opening. Some valves, usually known as normally closed check valves, require positive downstream pressure to open. Other valves, often called normally open check valves, require a positive backpressure to close. Reliability of a check valve can be improved by making the appropriate choice. Base your decision on whether the valve is open or closed more during normal system operation.
5. Maintenance
It is important to consider ongoing maintenance when choosing a valve, as this is essential for the reliability and stability of the application. Ball valves, for example, can resist clogging, jamming and malfunctioning but are not suitable for adjusting flow. Using ball valves to control flow can allow valves to leak or fail prematurely. The valve connection type can also lead to increased maintenance or replacement costs. Each connection type (threaded, barbed, push-in, Luer etc) has its advantages and disadvantages, so make sure you do your research!
