×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Filters & Control valves

Filters & Control valves

Filters & Control valves

(OP)
Hi (Question regarding sodium chlorate plant pump tank transfer)

We have a small tank (2 m3) that gets intermittent flow to it. From this tank we pump to the storage tanks. First we have the tank then the pumps (2 pumps pumping in parallel), then a control valve (control the 2m3 tank level by adjusting flow) then a cartridge filter and lastly the storage tank. We installed the filters in the system recently and also pressure transmitters before and after the filter. the purpose of these pressure tr. are to measure filter dP- but with the system as is it does not work. dP decrease then increase then decrease- and is very arratic the measurement- we cant use it as an indication to know when to change out the cartriges- the reason for this is is there is a control valve before the filter with a pressure drop of 170-220 kPA (20 % valve opening)- the pump tank incoming liquid is also "like pulsing" the way it comes. The pressure drop of the filter should iNCREASE to 30 kPa over a 12 hour period. We have similar filters sthe somewhere else but the set-up is differ:ent: Big tank (buffer & good head), No control valve the filters and then the next tank to which it transfers to.
We are thinking of moving the position of the control valve to after the filters to eliminate the variation in pressure measuerment - will this help?

Will there be a back pressure from the filters that will affect the dPs? i dont thinks so.
One thing- the two pumps are pumping in parallel but their impellor sizes are different - from what I understand they will fight each other- could this be a cause for the eratic pressure readings?

RE: Filters & Control valves

It sounds like you are trying to measure DP of a filter while the flow going through the filter is varying according to the level control algorithm. As the flow changes, so will the DP across the filter. In order for filter DP to make sense when deciding it is time to change it, the measurements must be made at the same flow rate.

Upstream or downstream of the control valve will give the same results.

Do you also measure flow in the line? If so, you can measure the filter DP at a given flow rate, and as the flow varies, you can compute what the DP would be at the same flow rate as the initial measurement. For simplicity you might start with your measurement at some flow rate that gives a good mid-scale reading on your DP transmitter. DP varies with the square of the flow. That is, at twice the flow, the DP will be four times as much. At half the flow, DP will be one-fourth as much.

A little experimentation and a little math will give you decent results.

I assume in all the above that your fluid is not compressible, does not change densities or flash at the valve, etc... In other words, it fits Bernoulli's law in the same way that water at reasonable flow rates with reasonable pipe sizes.

Good on ya,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources