FAQ - Ultrafiltration


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What happens if paint flow to an UF Element is allowed to stop?

The velocity of the ED paint slows to a stop, and then the solids begin to fall out of suspension. It is difficult to recover the UF membrane once the ED paint solids begin to accumulate inside the UF Element. The ED paint solids do two things, the first is that some of the membrane is blinded; secondly, the paint velocity in this region is reduced and so a larger area of the membrane suffers from poor permeate production.

What happens if I only have one pre-filter vessel before the UF Rack?

This pre-filter needs to be changed when the pressure differential exceeds the recommended value. In order to change the filter, flow must be stopped, which means the UF Elements are starved from ED paint during the change out time interval. In this situation, follow the manufacturer’s instructions to first purge the UF Elements of ED paint and then flush with buffered DI water. Take care to always to turn a paint valve handle slowly, otherwise damage can occur to the delicate UF membranes.

Should I bypass a single bag vessel during the bag filter change out?

No. Follow the instructions from the manufacturer of the ED paint system when changing the bag filters.

What is the typical life of a spiral-wound Element?

The typical life is about one year. In some cases an element can last up to 1½ years.

What happens if I change just one UF Element and all the other positions have old elements?

The new Element has the least amount of resistance to flow. The old elements have higher resistance to flow of ED paint. The new Element will allow a greater than normal amount of flow since the ED paint has a harder time going into the old elements. The permeate rate of the new Element will be very high at first. However, the new Element will suffer a short life due to the great volume of ED paint that goes through it.

Should I just change one or two Elements at a time?

No. For the longest life of all elements, change all the Elements at the same time. If the ages of the elements are similar, then they will have similar resistance to the flow of ED paint and work better as a team.

What does the term ‘flux rate’ mean?

Flux rate refers to the amount of permeate an UF Element can produce. The normal terms are either liters/minute or gallons/minute.

What is a UF Element?

Generally, a UF Element is the portion that can be removed and disposed of when the permeate rate can no longer be recovered by cleaning.

Does back flushing a UF improve the permeate rate?

Back flushing means to reverse the direction of the flow of the ED paint. This practice has not been very popular. It requires more initial expense to add the piping, valves and automatic controls. Not many customers have been able to justify the extra expense.

Does a UF Element require a pre-filter?

Spiral-wound UF Elements do require paint pre-filter. The filter size is typically 25 to 50 microns and sometimes even as small as 10 microns. Hollow fiber and tubular version typically do not require a pre-filter.

What are the major factors that affect permeate flux rate?

Percent solids of the ED paint, ED paint temperature, and velocity of ED paint past the face of the membrane.

What is MWC?

MWC is an acronym for Molecular Weight Cutoff. Some membrane manufacturer use this term to describe the typical opening size in the membrane. Values of 150,000 and smaller are typical for UF paint.

What are the major types of UF elements?

The different types are: tubular, hollow fiber, spiral, and plate & frame.

When ready to replace UF elements with newer (low VOC type) cathodic ED paints, is it best to replace several elements at a time?

This may not be a good plan as the new UF elements has less resistance to flow and thus take on a larger percentage than the older one they replaced. In most cases, this increased flow of ED paint with result in a shorter than normal life.

s it always a good practice to open the ED throttling valves (to the UF elements) full wide open?

Some customers report longer life if the ED paint flow is throttled back so the initial permeate rate is 110% of break-in permeate rate. For example, if the typical permeate rate for an 8” UF element on cathodic ED paint is 2.5 gpm, then limit the initial permeate rate to 2.5 gpm plus 10%, or about 2.8 gpm.

UF Element

When should I begin permeate flushing?

You should be immediately and set up a plan where each UF Module is flushed once a month. Each week another UF Element needs to be flushed and rested over the weekend before it is brought back on line the following Monday. The next Friday another UF Element is permeate flushed and rested in the same manner. This is repeated again with the next UF Element and so on. Then the next month the whole process is repeated all over again.

What if I do not want to spend the time and effort to permeate flush one UF Element every week?

Then be prepared to flush the UF Element at least when there has been a 20% decline in the permeate flux rate. You must also chemical clean when there has been a 30% decline. Many clients report that chemical cleanings are ineffective especially, the UF Element flux rate has declined more then and no permeate flushing was every performed

There was a power outage and the E-coat feed pump was turned off for some time?

This is a problem because the E-coat paint solids were able to settle inside the UF Element during the time that the E-coat feed pump was shut down.

What will happen if I close off the permeate discharge valves (V1*)?

If permeate valve is closed, then UF membrane will rupture away from its backing sheet and paint will leak into the permeate causing the UF Element to fail. The UF membrane is cast onto a backing sheet. The normal pressure gradient is from the side that the membrane is on to the permeate side. If the permeate side is closed Off, then the permeate side will begin to become pressurized so it may eventually become more that the membrane side causing the rupture to occur.

Why do I have to take 2 minutes to fully open valve (V10)?

This valve controls the entry of E-coat paint into the UF System. If this valve is opened too quickly then there will be an initial pressure imbalance between the exterior of the UF Element and the interior (since it has not had a chance to fill up, while the high pressure is allowed to encircle the entire exterior surface of the UF Element.

How long can I keep a UF element packed in RO or permeate?

Not a good idea in general. After about a week, bacteria will start to grow. Even if the element is flushed and replaced with fresh RO or permeate the bacteria will still be on the surface. We suggest a RO with 500ppm H2O2 flush and lock the membrane in the solution. Repeat weekly.

What should I use to pack a UF element?

Use a Propionic Acid Preservative which contains; 47.7% Glycerin, 47.7 % D.I. Water, 3.8% Propionic Acid and 0.8% Caustic Soda.

What is the anti-telescoping device (ATD)?

This appears to be shaped like a bicycle wheel that has spokes. The portions of the ATD that appear to look like the spokes actually keep the spiral membrane from being pushed out of position by the force generated by the E-coat paint as it enters the bottom end of the UF Housing.

What is the Baseline permeate flux rate?

This is defined as the permeate flux rate sometime after the initial startup, but not so long that the flux rate has started to decline significantly. The initial flux rates can be quite high sometimes, but allow 4 to 6 hours before recording a more stable and reliable value of the permeate flux rate.

What is PVDF UF membrane?

Polyvinyldiflouride (PVDF) is the standard polymer material used by most spiral UF manufacturers. This is a polymer that is cast onto a thin backing sheet. Once the polymer cures, the porous structure of the UF membrane has been established. It is through these small pores that the low molecular weight components in the E-coat paint can pass through.

Proper operation requires that the flow of E-coat paint flow through the UF be monitored closely so that it is held within the allowable range. Low E-coat paint flow results in low permeate flux rates.

It is possible to harm the UF Element of the flow of E-coat paint is too high. Take care when you take a UF Element Off Line to flush or clean it that you reduce the flow of E-coat paint accordingly.

What happens if I close the permeate discharge valve when E-coat paint is going through the UF Element?

The permeate will have no place to exit the UF Element and so after a couple of seconds the pressure on the backside (i.e. permeate side) will increase. This pressure increase on the backside of the membrane can be enough to cause rupture of the UF membrane from its backing sheet. This rupture event will result in an E-coat paint leak and the permeate will be discolored form the E-coat paint leak.

Should I throttle back the permeate discharge valve?

UFS does not generally recommend this practice. In some cases there may be a limit to amount of permeate storage capacity, which may be a reason for doing so, otherwise do not throttle back the permeate discharge.

Prefilter Bags

What happens if I run out of heat treated filter bags and I use an untreated filter bag either in the E-coat paint prefilter vessel or the CIP filter vessel?

Fine lint fibers will come off this style bag prefilter. These fibers will then be directed to the inlet of the spiral wound UF Element. These fibers will not be able to pass through the narrow flow channels and will wind up blocking off flow of the E-coat paint. This will shorten the service life of the UF Element and greatly reduce the permeate flux rate. The only thing that may help this is to reverse flush so that as many of these fine lint fibers are flushed out of the UF element and some relief can be achieved.

UF Rack

How do the groove type pipe clamps work?

There is a groove cut into each of the ends of the pipe where the groove clamp will be placed. The seal for the groove clamp is rather wide and is meant to straddle across where the two pipes come together. The groove clamps can tolerate some amount of mis-alignment and still not leak. If there is a persistent leak, then you must make sure the seal is not damaged correct any mis-alignment in the piping so that the two pipes share the same longitudinal axis and are straight and square with respect to each other.

What happens if the pressure in the E-coat paint feed manifold is about the same as the E-coat paint return manifold?

If the pressure gage reads about the same in both manifolds, then there is little of no flow of E-coat paint. This must be quickly corrected so that the proper pressure differential exists. You should begin by closing the butterfly valve on the return manifold (V9). Then you can either open or close the butterfly valve on the E-coat paint feed manifold valve (V10). Adjust until the proper pressure differential

If I have one or more UF Elements already operating on E-coat paint, how do I bring on line a UF Element that I just flushed or chemically cleaned?

This generally can be accomplished by first cracking open the paint discharge isolation valve (V3*). Keeping one hand on (V3*), place your other hand on the E-coat paint inlet isolation valve (V5*). Slowly taking 30 seconds or longer, open both (V3* and V5*) at the same rate until both valves are full open.

Why should I spend the money to purchase an expensive E-coat flow meter?

For low lifetime cost of any UF Element, the flow of E-coat paint must be closely controlled and monitored. Without a flow meter, it is practically not possible to know with certainly what flow rate is going into the UF paint feed manifold. Thus you are always guessing what the flow rate and will probably not get the longest life possible from your UF Elements.

UF Housing

I cannot remove the UF Element from the UF Housing?

This can occur if the E-coat bypass seals were placed on the bottom end of the UF Element and E-coat paint solids were allowed to settle above the seals, or maybe the piece of PVC pipe used was made has a thick wall and so the inside dimension is smaller than normal. In this case, you must remove the UF Housing from the UF Rack. Then remove the Bottom Cap and push the UF Element out of the Housing. Note – use a solution of permeate and solvent (approved by the E-coat paint supplier) to wipe down the inside of the UF Housing to remove any E-coat paint solids so the installation of the new UF Element is made easier.


Why can I only flush or clean one UF Module at a time?

The size of the CIP tank is sized to handle the turnover of one 8 inch UF Element and the CIP pump is only capable of producing enough flow to handle just one UF Element.

What is total UF System Cleaning?

This is a system that has a sufficiently large holding tank and a large enough pump that can provide the same flow conditions as the E-coat feed pump. Thus this system can be quite large and costly. Many companies cannot justify the expense of such a system that is used maybe every other month or so. Should I reverse the flow of the flushing or cleaning solution?


What is P3?

This is polyethyleneamine, a compound that is commonly available.

What does polyethyleneamine do?

When it is used as part of the final rinse after a chemical cleaning, it can impart a slight positive charge to the surface of the UF membrane. Since the E-coat paint solids are positively charged (only for cathodic E-coat paint) it is believed that the performance of the UF can be improved.

Does UFS recommend the use of polyethylene amine?

If you have experience with this and you believe it extends the interval between cleanings, then it will not harm the PVDF UF membrane.


The cleaning time is too short before the CIP is turned Off for high temperature. How can I increase the cleaning time? 1) Make sure that the low temperature set point is set for 46 C (115 F), or lower as previously reset. 2) Make sure the cooling water temperature is no more than ~18 C (65 F). 3) Make sure that the cooling water solenoid valve is properly working when the temperature controller turns it On. 4) Adjust the Lower temperature set point to a lower temperature so that the cooling water is used sooner. Do this especially if the ambient temperature is higher than ~27 C (80 F). 5) Ask to see if the cooling water temperature can be lowered.

The High Temperature (red light) is turned on and the CIP pump is not operating.

The high temperature limit has been reached and the CIP pump has been shut down. The UF Element can be damaged by high temperature as well as the PVC and other plastic parts that make up the CIP portion of the UF System.

Why does the flushing fluid or the cleaning solution get warm?

The CIP pump injects heat into the flushing or cleaning solution as the fluid is accelerated and moved by the pump impeller.

CIP Panel

Why is there a capacitor placed in parallel with the cooling water solenoid valve?

The purpose of the capacitor is to reduce the normal electrical arcing that occurs as the relay contacts come into contact and also when they are opened.

What does the ‘Power’ on green light indicate?

When this is illuminated, there is power to the CIP Pump.

What does the High temperature (red light) indicate?

When this is illuminated, the high temperature set point has been reached and the CIP pump has been turned Off.

What does the Cooling ‘On’ (green light) indicate?

When this is illuminated, the temperature of the permeate flush or the chemical cleaner solution is above the Low Temperature set point and the cooling water solenoid valve is turned On.

I press the red button to turn on the CIP pump, but it does not start?

Make sure the high temperature red light is not On. Make sure the power to the CIP Panel is OK. Restore power as required. Turn off power to the panel and have a qualified electrician inspect the motor starter. Reset the blue push button if the motor started was turned off. Have the electrician inspect the three heaters and replace as required. Make sure the contacts of the green (start) push switch operate and that there is not another wiring problem elsewhere in the control circuit of the CIP pump motor.

I press the red Stop button, but the CIP pump does not turn off?

There has been a wiring failure, problem with the contacts of the red (stop) push button, or other problem. Ask electrical maintenance to use the wiring diagram and trouble shoot the problem.


CIP turned OFF due to high temperature shutoff?

Wait for the red light to turn indicating the temperature of the permeate flushing or chemical cleaner solution has fallen below the high temperature set point. Turn off power to the CIP Control Panel. Open the Panel door (by qualified electrician who has been certified to perform electrical maintenance), locate the motor starter, depress the small blue reset button with a ‘R’ on its face.

CIP Pump has stopped and the heater(s) in the motor starter are open?

An overload was stopped when the heater(s) opened up. Check to see cause of overload and replace the heater(s) as required.