VIDEO: We get a lot of questions about Vacuum vs Peristaltic Portable Samplers for Water, Wastewater, Stormwater and Runoff Monitoring. This week we are looking at three leading providers of water samplers and sampling equipment. These water samplers use different sampling technologies and pumps to get the job done: ISCO 6712 vs Campbell Scientific vs Hach Sigma SD900. See the full comparison table of Peristaltic Vs Vacuum Portable Samplers.
Let’s take a closer look at Portable Vacuum Samplers vs Portable Peristaltic Samplers
Vacuum Portable Samplers
How Vacuum Portable Samplers Work
Vacuum sampler pumps create negative pressure or vacuum that draws the fluid from the water or liquid source and through the sampler. The vacuum sampler process includes:
- High Pressure Pre Sample Purge – A non-invasive yet high pressure air blast is used to purge or clean the intake tract of residual liquid and debris.
- Initial Draw – The water source is drawn through the intake hose by vacuum and then flows into the metering chamber.
- Filling & Metering – The metering chamber is now filled. The pinch valve remains closed while the system is pressurized. The remaining excess fluid is removed by vacuum until the correct sample amount is obtained.
- Sample Deposit – The sample is now at its precise volume and is then deposited into the sample container below.
- High Pressure Post Sample Purge – A high pressure yet noninvasive purge of air is used to thoroughly clean the intake tract of residual liquid and debris.
Vacuum Portable Sampler Advantages
- Precise Volume and Repeatability – The portable vacuum sampler’s metering chamber helps provide precise and repeatable sample volumes from start to finish. If the control volume is set at a level that does not greatly exceed the required sample volume, the suspended particles do not settle and affect the sample’s representativeness of the water source.
- No Tubing to Continually Replace – The tubing in a vacuum portable sampler is not squeezed repeatedly so it does not wear out as quickly as the tubing in a peristaltic pump sampler. There is no squeezing in vacuum portable samplers so the suspended solids in the fluid or water sampler are not altered.
- Larger Tubing & Volume = More Representative Sample – Unlike the smaller 1/4″ or 3/8″ tubing found on peristaltic pump portable samplers, vacuum pump portable samplers are typically compatible with larger tubing. This larger 3/8″ or 5/8″ sample tubing allows larger suspended solids to pass directly into the sample container without being disturbed. Smaller tubing, on the other hand, may become blocked by larger solids or filter out material that should be sampled.
- Greater Velocity – Vacuum pump portable samplers typically provide greater velocity when compared to peristaltic pump portable samplers. The greater velocity of portable vacuum samplers holds particles in suspension better and provides a more representative sample.
- Lower Cross Contamination through High Pressure Post Purge – The cleansing air pumped through a portable vacuum pump sampler is under higher pressure than the air pumped through a portable peristaltic pump sampler. The high pressure air may provide a more thorough tubing purge and help eliminate the risk of residual liquid being combined from a previous sample.
Vacuum Portable Sampler Disadvantages
- Higher Power Requirements – A typical vacuum pump based portable sampler requires more power to run than a peristaltic pump sampler. This translates into larger batteries or power supplies to power the pump for the duration of the sampling interval. This may also translate into a higher transport weight with some brands of vacuum based portable samplers.
- Increased Height – Some portable vacuum samplers may be taller due to the larger sample or metering chambers. Added height can also be due to the vacuum / sample tract requirements.
Peristaltic Portable Samplers
How Peristaltic Portable Samplers Work
- The peristaltic pump rotates first in the reverse direction to purge the hose. By pumping air through the system, the pump cleans the intake tubing of residual liquid and obstructions. A clean water source can also be used to purge the line.
- The peristaltic pump then spins in the forward direction and pumps the liquid or water from the source into the intake tubing.
- The controller then detects the fluid in the intake tubing and determines how many pump counts or revolutions are needed to achieve the programmed sample volume.
- The pump continues to rotate forward for each pump count until it reaches the required sample volume. The pump tubing is squeezed to move the fluid along with each pump rotation.
- The sample continues to be deposited in the sample container until the required pump counts are completed.
- The pump now purges the line by rotating in the reverse direction. This reverse action pumps air through the system and cleans the intake tubing of residual liquid and debris.
Peristaltic Portable Sampler Advantages
- Less Power – Peristaltic pump samplers normally require less power to run than a vacuum pump sampler.
- Lower Profile – no wires or vacuum tubes stick out from a peristaltic pump sampler so the sampler can have a lower height.
- Cheaper Initial Acquisition Cost – Peristaltic pump samplers may be less expensive to initially procure than vacuum pump samplers.
Peristaltic Portable Sampler Disadvantages
- Tubing Wears Out – By repeatedly squeezing the tubing to move the fluid through the sampler, the tubing just wears out and the squeezing become less tight. The sample volumes then start to vary and from one sample to the next.
- Sample Representation May Not Be Accurate – When the peristaltic sampler tubing is squeezed, the suspended solids in the sample can be altered and squeezed as well. The solids may then stick to the inside of the tubing causing the recorded sample to not be truly representative of the water source at that time.
- Smaller Tubing Size – Many peristaltic based samplers are not compatible with larger 3/8″ or 5/8″ tubing. When smaller 1/4″ or 3/8″ tubing is used to sample, it can become blocked by large debris or suspended solids in the water. Large solids may also become screened out by the smaller diameter hose.
- Lower Transport Velocity – Peristaltic pump samplers typically provide less velocity than vacuum pump samplers. Particles tend to drop out of suspension with the lower velocity of peristaltic samplers. If the solids settle, this may cause the water sample to be misrepresentative of the water source.
So what do you see as the main differences between vacuum based samplers and peristaltic samplers? What advantages are most important for you with vacuum samplers? What are the most important advantages of peristaltic samplers for you? Let us know in the comments below.
Disclosure: Aqua Technology Group uses ISCO, Hach Sigma, Manning and Campbell Scientific and other water sampling equipment regularly in our consulting, repair and service work. store.aquatechnologygroup.com distributes samplers.