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Thread: Grinder pump question

  1. #16
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    Quote Originally Posted by ballvalve View Post
    Just so the world understands hydraulics, INCREASING pipe size reduces friction and thus head loss. If your pipe is 1/8" or 20" and 50' tall, the pressure gauge at the bottom is reading the same for both pipes.

    In fact, if he had a 200 foot run he would HAVE to increase pipe size to reduce head loss.
    Infact he would not have to increase the size of the pipe for a 200' run. Please understand that water is heavy approx 8 pounds a gallon......increasing the pipe size increases the water in the pipe and that increases the head pressure the pump must overcome.. We are speaking of a FORCED HIGH PRESSURE SEWER MAIN. Increasing the pipe size is counter productive.



    Too big can be just as bad as too small. Take it froma guy who has installed 100's of high pressure forced sewers.

    What size pipe do you think the city has for their forced main sewers with literally hundreds of grinders connected to it? Most around here are 2" for the typical neighborhood st with hundreds of homes connected.

    For example I will use a small grinder......such as the saniflow toilet system. It calls for a 3/4 or 1" drain. If you increase the size of the drain to 1.5" the pump will not produce enough power to overcome the head pressure.

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    The last grinder I installed was a duplex system with a 48"x60" basin. The pumps would alternate in operation as to keep both pumps exercised. This system was a 4 float system,consisting of on,off,reset and high water.Each pump has its own stop valve and check valve and connect to a common 1.25" tee and then discharges out of the tank 1.25".
    I was specifically instructed by the design engineer not to exceed a 1.5" pipe diameter and doing so would increase the head pressure on the pump.

    Basically on a high pressure forced sewer your pump has to be strong enough not to just have enough head pressure to pump it to the city......your pump has to have enough power to exceed the head pressure of the citys main also and that can have 75# of head pressure. I had one that exceeded 125 pounds and the city had to add another lift station to relieve the pressure so we could get a pump that would be powerful enough without spending 3 times as much.
    Last edited by Hackney plumbing; 01-13-2012 at 02:52 PM.

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    General Engineering Contractor ballvalve's Avatar
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    In fact he would not have to increase the size of the pipe for a 200' run. Please understand that water is heavy approx 8 pounds a gallon......increasing the pipe size increases the water in the pipe and that increases the head pressure the pump must overcome.. We are speaking of a FORCED HIGH PRESSURE SEWER MAIN. Increasing the pipe size is counter productive.
    Sir, I risk being unkind about your understanding of hydraulics and water flow through pipes. Therefore, I hope that valveman or someone better educated in the flow of water in pipes [fairly well defined prior to the 1800's] will give you a bit of information. I would probably do it in an unkind manner.

    Forced high pressure mains is IRRELEVANT to this discussion. Once again, a 20 foot diameter pipe provides far less restriction to flow than a 1.5 or 2'" pipe. The 20' diameter pipe gives exactly the same reading on a pressure gauge at 500' height as the 1/4" line. Have a look at Agricola's mining engineering book from 1572. He describes this 'phenomena' in very good detail. I have that first edition in Latin and the translation by our ex president Hoover, a scholar in Latin. Physics has not changed since, no matter if one installs "high pressure grinder pumps".

    If you are trying to discuss the need to keep solids in suspension due to flow VELOCITY, and not to settle in a 20 foot diameter pipe, then I understand the point.

    Your engineer was either missing a few cylinders, did not explain his logic to you in a correct manner, or [as it should be interpeted] he wanted you to use the smaller pipe size to keep a specific flow rate so that solids and weighted matter did not drop out of suspension.
    Last edited by ballvalve; 01-14-2012 at 04:04 PM.

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    Quote Originally Posted by ballvalve View Post
    Sir, I risk being unkind about your understanding of hydraulics and water flow through pipes. Therefore, I hope that valveman or someone better educated in the flow of water in pipes [fairly well defined prior to the 1800's] will give you a bit of information. I would probably do it in an unkind manner.

    Forced high pressure mains is IRRELEVANT to this discussion. Once again, a 20 foot diameter pipe provides far less restriction to flow than a 1.5 or 2'" pipe. The 20' diameter pipe gives exactly the same reading on a pressure gauge at 500' height as the 1/4" line. Have a look at Agricola's mining engineering book from 1572. He describes this 'phenomena' in very good detail. I have that first edition in Latin and the translation by our ex president Hoover, a scholar in Latin. Physics has not changed since, no matter if one installs "high pressure grinder pumps".

    If you are trying to discuss the need to keep solids in suspension due to flow VELOCITY, and not to settle in a 20 foot diameter pipe, then I understand the point.

    Your engineer was either missing a few cylinders, did not explain his logic to you in a correct manner, or [as it should be interpeted] he wanted you to use the smaller pipe size to keep a specific flow rate so that solids and weighted matter did not drop out of suspension.
    With a forced main you have check valves at the city connect and at the pump. The pump must overcome the head pressure pushing back on those two check valves froma dead start. Do you think two 2" check valves would be easier to open rather htan 1.5" check valves with a constant head trying to keep them closed? If larger pipe is better why dont we use 3" pipe with 3" check valves......how much force would it take to open a three inch check valve with 75 psi pushing on the otherside? Do the math on the area of a 3" check then multiply the sq inch area......75 pounds is pushing on each square inch.

    Sure larger pipes have less friction but thats not the only consideration when pumping into a high pressure sewage main with a grinder pump.

    Also with a larger pipe,solids would collect and stick to the walls of the pipe.......it would not clean itself properly.

    A 1.5" diameter pipe has 1.767 sq in of area. A 2" pipe has 3.142 of area.Thats a difference of 1.375 sq in more area for the 2". With 2" check valves installed it would require the pump to develop 78% more force to open the 2" check valve. compared to the 1.5"......and you have two check valves.

    I copied this below from copper.org. I wouldn't use copper for a grinder installation but for friction loss purpose,it proves a point.
    .................................................. .................................................. .........................
    Table 6, page 30, shows the
    relationship among flow, pressure
    drop due to friction, velocity and tube
    size for Types K, L and M copper
    water tube. These are the data required
    to complete the sizing calculation.

    NOTE: Values are not given for flow
    rates that exceed the maximum
    recommendation for copper tube.For the tube sizes above about
    11/4 inch, there is virtually no difference
    among the three types of tube in terms
    of pressure loss.

    This is because the
    differences in cross sectional area of
    these types become insignificant as tube
    size increases. In fact, for this reason, the
    value for Type M tube given in Table 6
    can be used for DWV tube as well.
    Last edited by Hackney plumbing; 01-14-2012 at 08:21 PM.

  5. #20
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    Quote Originally Posted by ballvalve View Post
    Just so the world understands hydraulics, INCREASING pipe size reduces friction and thus head loss. If your pipe is 1/8" or 20" and 50' tall, the pressure gauge at the bottom is reading the same for both pipes.

    In fact, if he had a 200 foot run he would HAVE to increase pipe size to reduce head loss.
    Lets take your example of a 200' forced main sewer and really see if the pipe size needs to be increased. It will be fun!!!! I promise. Ok,the grinder pumps I install we use sch 40 pvc pressure pipe main line from the pump basin to the city connect. Typically this is buried 12-18" deep in my area.

    Now what would be the friction loss of 1.5" pvc for a 200' run compared to a 2" pvc 200' run? Well friction loss depends also on the velocity of the sewage being pumped amoung other things like temp,viscosity etc. but we are not concerned with those right now,just friction loss at a certain flow rate. I beleive the last pump I installed was pumping 15 gpm so that is what I will use in this example regarding friction loss for our high poressure sewer main.

    According to Charlotte pipe,1.5" pvc at a flow rate of 15gpm has a friction loss of .66 psi per 100' of pipe. We have 200' run so lets double the .66psi and that gives us a 1.32 psi pressure drop from friction. WOW a whole pound and a half!!!! LOL

    Ok lets do the same for 2" sch 40 pvc. Its friction loss at a flow rate of 15gpm per 100' of pipe is .19psi. For a 200' run,the total pressure drop from friction would be .38 psi....not even a 1/2psi is lost due to friction.

    So like I said no pipe size increase would be needed for a 200' run. It makes no sense to increase the pipe size from 1.5" to 2" to save 1psi pressure loss from friction.......espcially when the check valves in the 2" line would be harder to open when the pump kicks on with a static head keeping them closed. The 2" check valve has more surface area and would require more force to open compared to a 1.5" check. Approx 78% more area for the 2" vs the 1.5" check valve. The one psi you would gain by using 2" pvc would be lost due to the check valve issue.

    I hope this helps you.

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    General Engineering Contractor ballvalve's Avatar
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    http://www.spiraxsarco.com/resources...eck-valves.asp

    Have a read about check valves. But mainly you need to understand that a larger check valve does not require any larger forces to open, unless it is designed to have a high pressure spring for fast closing. the only issue is that the check valve be designed to a proper size for the FLOW rate, so that it does not 'chatter'. A 12" check valve opens at the same rate as a 2" check valve, provided that the pressure entering the valve exceeds the static head pressure on the 'other' side of the check valve.

    I would suggest looking at some basic hydraulic text books for an understanding of this.

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    Quote Originally Posted by ballvalve View Post
    http://www.spiraxsarco.com/resources...eck-valves.asp

    Have a read about check valves. But mainly you need to understand that a larger check valve does not require any larger forces to open, unless it is designed to have a high pressure spring for fast closing. the only issue is that the check valve be designed to a proper size for the FLOW rate, so that it does not 'chatter'. A 12" check valve opens at the same rate as a 2" check valve, provided that the pressure entering the valve exceeds the static head pressure on the 'other' side of the check valve.

    I would suggest looking at some basic hydraulic text books for an understanding of this.
    Now that you understand that a 2" pipe doesn't offer any real advantage over 1.5" pipe for frictions loss at the flow rates for a forced sewer.......please understand that the larger the surface area is the more sq inches it contains........PSI stands for POUNDS PER SQUARE INCH.....of what? OF PRESSURE!!!!!!!. So with more sq in of area.......the force exerted on that object is greater. Dont you realize the 2" check valve has more surface area to be acted upon by the head pressure on the other side of it???
    why do you think 1/2 pipe has a much higher pressure rating than 8" ??????????? Riddle me that. LOL

    By the way.....you dont install spring type check valves in a forced sewer. LOL
    Last edited by Hackney plumbing; 01-15-2012 at 03:31 PM.

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    Just a quick question...anyone feel free to jump in. If you were asked to open a door that was being acted on the other side with 75 psi (pounds per square inch) do you think it would be easier to open a door that was 2 sq ft or 4 sq ft?

    Keep in mind for every square inch of door area there is 75 pounds per square inch pushing back on it.

    The pressure is the same but there are MORE square inches for the pressure to act upon the object,in this case the example was a door.

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    General Engineering Contractor ballvalve's Avatar
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    That makes as much sense as a horse with wings.

    Any size door with 75 psi behind it will open at 75.00000001 psi on the opposite side, dependant only upon the friction in the hinges.

    Valveman, how about explaining that to him?

    And a good plumber will always use a check valve 1 or 2 pipe sizes larger than the main run, due to the large head losses and turbulence caused by most of the designs.

    why do you think 1/2 pipe has a much higher pressure rating than 8" ??????????? Riddle me that. LOL


    Are you inquiring about schd 40 PVC, radiator hose, 8" agricultural PVC 25 pound head pipe, Yellowmine o-ring joined mining PVC, steel gas line, oil well drill pipe, or aquarium tubing?
    Your question is a riddle.
    Last edited by ballvalve; 01-16-2012 at 02:04 PM.

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    Quote Originally Posted by ballvalve View Post
    That makes as much sense as a horse with wings.

    Any size door with 75 psi behind it will open at 75.00000001 psi on the opposite side, dependant only upon the friction in the hinges.

    Valveman, how about explaining that to him?

    And a good plumber will always use a check valve 1 or 2 pipe sizes larger than the main run, due to the large head losses and turbulence caused by most of the designs.



    Are you inquiring about schd 40 PVC, radiator hose, 8" agricultural PVC 25 pound head pipe, Yellowmine o-ring joined mining PVC, steel gas line, oil well drill pipe, or aquarium tubing?
    Your question is a riddle.
    The larger check valve will chatter......the pressure varies not only static but also the dynamic pressure varies while the pump is operating. There is absolutely no benefit upsizing the pipe from 1.25 at the pump to 2" service line and then connect to a 1.25 or a 1.5" forced sewer tap. Absolutely NONE. Solids would collect on the side walls and the head pressure would be worse. 1.25 and 1.5 will stay clean naturally by the action of the pump. This will cause alot of turbulence and ALOT of friction loss.

    Dont you understand the difference in the friction loss at the pump rates a forced main uses over a 200 ft distance is only about 1 psi? And that would be lost by the turbulence your larger check would create and the walls of the pipe would get sticky causing even more pressure loss than a smaller 1.5" pipe.

    So to sum it up.....Its not a good idea at all to increase the pipe size to 2" connecting to a 1.25" sewage pump connecting to a 1.5" forced sewer. No matter what the distance......if the friction loss becomes to great,you increase the size of the pump and the line your connecting to at the city.

    Try looking at the difference between the max pressure 1/2" compared to 8" of copper or pvc.

    Increasing the size of the checks is a waste of time and money and causes turbulence/friction loss. It also can chatter,especially in a forced sewer.

    Pumping to an open pipe is totally different than pumping into a pipe with substantial head pressures.
    Last edited by Hackney plumbing; 01-16-2012 at 03:45 PM.

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    In a forced sewer application the pump turns on and starts to pressurize the outlet pipe and starts to flow that builds pressure. This pressure acts on the flap of the check valve when it build enough head and flows into the citys main. The problem is the pressure can surge in the city main and often does when another seweage grinder starts to operate. The pump does not respond as quick as the pressure surge and the check valve slams shut then the pump builds enough pressure to open it back and this cycle repaeats over and over and destroys your check valve.

    Dont over size your swing checks in a forced main or you will be sorry. A forced system is a very dynamic system and has a life of its own with pressures and flow both being considerations.

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    So to sum it up.....Its not a good idea at all to increase the pipe size to 2" connecting to a 1.25" sewage pump connecting to a 1.5" forced sewer. No matter what the distance......if the friction loss becomes to great,you increase the size of the pump and the line your connecting to at the city.


    Without posting a pipe flow rate and friction calculator here, "no matter what the distance" [and one may assume you mean the head as well] is incorrect. Unless you can find a grinder pump that outputs 300 or 400 PSI, you will need INTERMEDIATE pump stations on long runs and high heads in order to preserve your belief in 1.5" pipe. I hope you know that at a certain point in length and head, a pump outputting even 500 psi will allow a little pee type stream to exit the pipe. I don't think your sewage or tie in would be particularly successful with your theory.

    you increase the size of the pump and the line your connecting to at the city.


    What does that mean, increasing the size of the line you are connecting to at the city?

    Good to see you didnt go back to the PSI to open a door issue.

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    Quote Originally Posted by ballvalve View Post

    Without posting a pipe flow rate and friction calculator here, "no matter what the distance" [and one may assume you mean the head as well] is incorrect. Unless you can find a grinder pump that outputs 300 or 400 PSI, you will need INTERMEDIATE pump stations on long runs and high heads in order to preserve your belief in 1.5" pipe. I hope you know that at a certain point in length and head, a pump outputting even 500 psi will allow a little pee type stream to exit the pipe. I don't think your sewage or tie in would be particularly successful with your theory.



    What does that mean, increasing the size of the line you are connecting to at the city?

    Good to see you didnt go back to the PSI to open a door issue.
    The e/one grinder pumps will pump horizontal through a 1.5" pipe for over 4,000 ft. If it had to go further the answer would never be increasing the size of the forced main on the customers property.......it would require a bigger pump and the bigger pump would have a larger outlet. You simply never just increase the customers service line.


    It means the city would need increase the size of their line to match the size of your line. You'll never see a 2 or 3" lateral line for the typical property...those are the size lines you find out in the main lines the city uses.

    The door under water is exactly true. Until the pressure equalizes on both sides of the door the larger door will be much harder to open than the smaller one because theirs more surface area for the pressure to act on.
    It really wouldn't be a problem if the citys pipe would maintain a constant pressure but it doesn't......the citys pressure varies ALOT. One second the main may have 100 psi 1/2 second later its 60 psi then maybe up to 80.....etc etc. This will cause all types of problems with over sized check valves and the pump itself.

    Thats why you get the system engineered with the help of the system provider and you do not deviate. They know what works on their system now and what will work in the future as they design the sytem and more homes are connected. If you just go buy a pump that will work today with the system it may not work tomorrow when another house is added to the line and the pressure increases. You would simply have to replace the pump every time they added more people to the sewer. Thats why the city is specifying the pump and the size lines. If you follow their specifications and next year the pressures are too great for your pump to work.......THEY will have to get the system back to the specs and pressures it was designed for. So while you may get by with a cheaper pump today,next week you may be buying another one if you do not follow the specs.

    To sum it up you simply do not size a forced sewer main like you do a water main. You do not worry about friction loss due to pipe size. You use the size line the city haprovided for the tap connection at the street. Over sizing WILL cause problems. The pipe will not clean itself and chat chat chat chattering swing checks that can damage the check valve and make the pump work harder.

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    The reason why I said at any distance is because the pump has no problem pumping the typical distances for a home. For the E/one pump a couple hundred feet is not even worth talking about......1 psi loss is not an issue. The E/one pump has a cut off head of 185' and can generate up to 40% more for up to 5 minutes. Its pump curve is almost VERTICAL. It has a 1.25" outlet.

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