Is it normal to lose pump prime each time you change your sand filter valve position?

[guitargeekrich]

Hi all, brand new pool owner here. On my setup (details below) each time I change the position of my filters multi position valve my pump completely/rapidly loses prime (I can hear the water draining back into the pool). PB says this is normal, but wanted to get second opinions from you fine experts.

Pump holds prime fine under normal start/stop conditions.

- speck variable speed pump, 2.7 THP
- pump is above pool level maybe a foot, no flooded suction
- pentair sand filter

I also had a question about these pentair quarter turn valves. I see they can be adjusted to multiple positions. Is it possible the PB installed them in such a way that they can't be fully closed?

Thanks in advance for the help!

 

[PoolStored]

Hi all, brand new pool owner here. On my setup (details below) each time I change the position of my filters multi position valve my pump completely/rapidly loses prime (I can hear the water draining back into the pool). PB says this is normal, but wanted to get second opinions from you fine experts.

Likely to rebuild the MPV...or at least be ready. There are a number of o-rings in the MPV that seal the valve. If it happens when you turn it, the seal is being lost...likely through the MPV. So o-ring, or spring or a combination.

My system started doing that this year when I move from filter to backwash. I have the parts to rebuild at the end of the season this year. It too primes and runs fine.

Always turn your pump off when changing the MPV position.

I also had a question about these pentair quarter turn valves. I see they can be adjusted to multiple positions. Is it possible the PB installed them in such a way that they can't be fully closed?

Yes, it is possible. It is also possible to change the position of the valve so that it will close.

Take a picture of the valve, with the handle in both extreme positions. Next, take the handle off and take a picture. We'll help you out.

 

[guitargeekrich]

Thanks, I'll get those pictures tomorrow when it's light out.

As for the MPV, it's a brand new pool. I'm guessing they left an oring out. I will discuss with the PB.

 

[Bperry]

Thanks, I'll get those pictures tomorrow when it's light out.

As for the MPV, it's a brand new pool. I'm guessing they left an oring out. I will discuss with the PB.

Your turning the pump off before moving the MPV, correct?

 

[guitargeekrich]

Hi all:

Here are a few photos of my setup. Note that the stops on the valve body in combination with the pin locations on the removable handle yield a quarter turn (from 9 o'clock open to 12 o'clock - which is presumably closed albeit I am suspicious the valve(s) are still open - see Pic 3).

@Bperry to your question - yes, I don't modify the MPV while the pump is in operation.

ETA: The valve stems seem fine, there is a normal amount of resistance when moving the valve handles

Pic 1: Valve open (off label at 9 o'clock) with handle removed


Pic 2: Valve open with handle attached


Pic 3: Valve maximum range of motion presumably in a closed condition


Pic 4: System in normal filter operation

 

[PoolStored]

Valves look to be correct and you have them labeled as open and closed correctly.

 

[wireform]

My take on your problem is before rebuilding the mpv I'd look at each of the four collar nuts, two at the filter, inlet and outlet and the two either side of the salt cell. Those all have a gasket which can cause what you described when the seal isn't doing its job. I'd back off one at a time and do a quick inspection if any of them have a split but are just stuck in the groove. Before closing them back up very snug hand tight I'd lube it well.

 

[guitargeekrich]

Thanks guys/gals - this is really helpful.

I'm still stumped if the valves on the suction side of the pump are configured properly - where is the water going when I close them prior to opening the pump strainer lid or change the MFV position?

With all 3 of those valves closed, the water level in the pump still drops like a rock if I open the pump lid or "depress" the MFV handle. Is it possible there is a vacuum that pulls the water out of the pump discharge caused by water draining back into the pool via the returns?

There aren't any noticeable leaks on any of the gaskets/unions on the filter or salt cell - although it has rained constantly since Thursday so that might be hiding it some. But I started up the system on Monday of last week and had a few days of dry weather without noticing any leaks.

I will play out some more "experiments" today after work.

 

[1poolman1]

Thanks guys/gals - this is really helpful.

I'm still stumped if the valves on the suction side of the pump are configured properly - where is the water going when I close them prior to opening the pump strainer lid or change the MFV position?

With all 3 of those valves closed, the water level in the pump still drops like a rock if I open the pump lid or "depress" the MFV handle. Is it possible there is a vacuum that pulls the water out of the pump discharge caused by water draining back into the pool via the returns?

There aren't any noticeable leaks on any of the gaskets/unions on the filter or salt cell - although it has rained constantly since Thursday so that might be hiding it some. But I started up the system on Monday of last week and had a few days of dry weather without noticing any leaks.

I will play out some more "experiments" today after work.

As long as there is water in the pump up to or near the inlet the pump is primed. Any time you move the MPV you open a port to the atmosphere, allow air in, and the water to drain back somewhat. With the inlet plumbing above the inlet port, as yours is, you really shouldn't lose much water from the pump at all.
Speck makes a great pump, you just don't see many of them.

 

[guitargeekrich]

As long as there is water in the pump up to or near the inlet the pump is primed. Any time you move the MPV you open a port to the atmosphere, allow air in, and the water to drain back somewhat. With the inlet plumbing above the inlet port, as yours is, you really shouldn't lose much water from the pump at all.
Speck makes a great pump, you just don't see many of them.

Thanks poolman.

What I'm seeing is that when I move the MFV and break the seal to atmosphere, the head from the pump discharge pushes the water back through the pump and into the pool and I end up having to reprime. You're telling me that's normal? Maybe I misunderstood, but someone above indicated that the MFV should maintain a seal to prevent air intrusion when moving it's position?

I did confirm that the valves on the skimmer and main drain lines are sealing properly, so I'll just add the closing of those valves to my backwash procedure to keep the pump primed.

As for the pump, PB initially told me I was getting a penatir pump but that's what showed up. I checked around and the consensus was that it was on par with pentair from a quality perspective and I liked the interface, so I just went with it. I originally assumed it was a rebrand of one of the more well known pumps. Can't go wrong with German engineering!

 

[Homebrewale]

I don't see why water wouldn't drain back into the pool. When the MPV is moved from Filter to Backwash, the system goes from closed to open. It would be like holding a bottle of water upside down in the pot of water. The water stays in the bottle. Then you take a sharp object and poke a hole in the bottle. The water all drains out. What I do is shut off the pump, close the supply side valve that is before the pump, turn the MPV to Backwash, hit the start button on the pump, and then as the pump is starting up, reopen the supply side valve. Otherwise, water in the pump basket flows back into the pool and my pump needs to prime again which takes several minutes since there is about a 3' elevation difference between the pump and pool.

 

[1poolman1]

Thanks poolman.

What I'm seeing is that when I move the MFV and break the seal to atmosphere, the head from the pump discharge pushes the water back through the pump and into the pool and I end up having to reprime. You're telling me that's normal? Maybe I misunderstood, but someone above indicated that the MFV should maintain a seal to prevent air intrusion when moving it's position?

I did confirm that the valves on the skimmer and main drain lines are sealing properly, so I'll just add the closing of those valves to my backwash procedure to keep the pump primed.

As for the pump, PB initially told me I was getting a penatir pump but that's what showed up. I checked around and the consensus was that it was on par with pentair from a quality perspective and I liked the interface, so I just went with it. I originally assumed it was a rebrand of one of the more well known pumps. Can't go wrong with German engineering!

Unless every bit of water is removed from the pump basket, the pump is "primed" as long as the water in the basket is at, or very close to, the bottom of the pump inlet. There is confusion about what a "prime" actually is. That is why VSPs have what they call a priming cycle of up to 8 minutes each time the pump starts. It takes the water in the basket, the "prime" and removes it quickly, creating an area of very low pressure allowing the weight of the atmosphere to push water into the pump, even uphill as most pumps are at least a foot above the water level. Once the water starts to flow the impeller keeps it moving. That's the simple explanation and also why, at higher elevations, a pump can't move as much water. Less atmospheric pressure.

You have to break the "seal" in the MPV each time your use it. When you remove the pressure on the gasket in the MPV, it lifts the entire diverter and opens all ports, for a moment at least, to the backwash port, which is an open line, quickly pulling air to enter the system as the water in the filter starts to fall back to the pool as it is easier than trying to get through the filter media to the pool. Your filter is higher than the pump, the water in the filter is higher than the pump. It then acts like a drinking straw that you have placed your finger over. Lift the straw out and the liquid will stay in the straw. Remove your finger, air in the top, liquid out the bottom. Same principle. It is completely normal.

There is too much worry about air getting into a system. It is normal, it happens every time you open the pump to clean the basket and, unless there is a suction leak, will be almost completely removed when the pump starts up again. If there is a suction leak you fix it, if not you ignore it.

At a certain age, virtually all systems I have ever seen, including my own, will develop very small leaks that don't let water out but will allow air to be pulled in each time the pump stops. I can purge air every time the pump starts, if I was up at 2:00AM, but there is no need. I could completely replumb the system, install all new O rings and gaskets, but why? Worrying about a small amount of air getting into a system that, despite what you hear is not completely "sealed," does not make the pool trouble free. But, its your pool, your money, your choice.

 

[guitargeekrich]

I don't think I've explained myself very well (reading my original post I didn't describe the problem properly) - it's not the changing to backwash/rinse that causes the system to vent that seems abnormal. That makes perfect sense, I'm moving the valve to plumb to atmosphere.

Its that if I don't rotate the MPV at all and just depress the handle (keeping it in the filter position) it vents also to atmosphere and I lose prime. That's why I was intrigued when someone above mentioned a potential issue with an o-ring or seal in the valve. I would think it would maintain a closed system until you turned the valve handle.

It seems though that everything may be behaving as it should. What confused me the most is that the first time I cleaned my pump strainer basket I closed the suction side valves before removing the lid and as soon as I opened the pump the water level in the basket dropped. I attributed it at the time to thinking the quarter turn valves on the skimmer/drain lines were't configured right (I saw that the stops on the valve handle could be moved to different positions). But what must have happened is that when I opened the basket the water in the return to the jets moved back into the pool and siphoned water out of the pump discharge. I wouldn't have expected it to do that with the filter in between the pump and the pool.

I appreciate everyone's input and help getting me up to speed!

 

[guitargeekrich]

Unless every bit of water is removed from the pump basket, the pump is "primed" as long as the water in the basket is at, or very close to, the bottom of the pump inlet. There is confusion about what a "prime" actually is. That is why VSPs have what they call a priming cycle of up to 8 minutes each time the pump starts. It takes the water in the basket, the "prime" and removes it quickly, creating an area of very low pressure allowing the weight of the atmosphere to push water into the pump, even uphill as most pumps are at least a foot above the water level. Once the water starts to flow the impeller keeps it moving. That's the simple explanation and also why, at higher elevations, a pump can't move as much water. Less atmospheric pressure.

You have to break the "seal" in the MPV each time your use it. When you remove the pressure on the gasket in the MPV, it lifts the entire diverter and opens all ports, for a moment at least, to the backwash port, which is an open line, quickly pulling air to enter the system as the water in the filter starts to fall back to the pool as it is easier than trying to get through the filter media to the pool. Your filter is higher than the pump, the water in the filter is higher than the pump. It then acts like a drinking straw that you have placed your finger over. Lift the straw out and the liquid will stay in the straw. Remove your finger, air in the top, liquid out the bottom. Same principle. It is completely normal.

There is too much worry about air getting into a system. It is normal, it happens every time you open the pump to clean the basket and, unless there is a suction leak, will be almost completely removed when the pump starts up again. If there is a suction leak you fix it, if not you ignore it.

At a certain age, virtually all systems I have ever seen, including my own, will develop very small leaks that don't let water out but will allow air to be pulled in each time the pump stops. I can purge air every time the pump starts, if I was up at 2:00AM, but there is no need. I could completely replumb the system, install all new O rings and gaskets, but why? Worrying about a small amount of air getting into a system that, despite what you hear is not completely "sealed," does not make the pool trouble free. But, its your pool, your money, your choice.

Thanks for your reply!

As a new pool owner, I guess it's just going to take some time to understand what "normal" looks like. I'm comfortable working with hydrodynamic systems, but have never put my hands on a pool sand filter until last week. I do industrial automation for pool money. Pumps, motors, drives, controllers, etc. are very familiar to me. I got excited when I saw the drive manual for the pump that it supports Modbus RTU! But it's the little things like those 1/4 turn valves with various stop configurations that made me feel like a doofus, or not knowing what's really going on inside that sand filter.

I appreciate the time everyone has taken out of their day to help set me straight!