Tools Some advice on my compressor please.

Discussion in 'Tools & Equipment' started by k20a3, Sunday 5th Jun, 2016.

  1. k20a3 Valued Contributor ★ ★ ★ ☆ ☆

    Hi all,

    I have plumbed in my new compressor and all is well. It's a Clarke SE18C200ND. It has a 200L tank, CFL rating of 18 and has a 4hp motor. My dad did the electrics (62 amp 10mm2 cable ) and it runs superbly. Wondered if anyone else here has one as apparently they are a popular model.
    Being new to using compressed air and air tools I am supprised that it still needs to charge so quickly when using cut off tools and a die grinder. I haven't timed it yet but after about 40 - 60 seconds of use the pressure is down to around 95 psi and it charges. No wonder people say buy the biggest you can :shock:

    I am not disappointed as it easily charges and cuts off even when using the tools. I wondered how hard a use any of you give such a compressor. It's rated as industrial but when I emailed machine mart to see what duty cycle it had, they said about 6 charges per hour was about right. Didn't seem that good to me? I think it must be heat that's the issue as they do feel hot after a charge. I wondered if I got a decent industrial type fan and had it constantly blowing over the pump which would cool it quicker, could I then give it more use?

    What do you folks think?

  2. jimjams Club Member ★ ☆ ☆ ☆ ☆

    I would have thought that the duty cycle depends on the rate of use of the air used by the connected air-tool. So if the air-tool uses a lot of air, the compressor will have to keep coming on. Not sure about the heat dissipation, but yes if the compressor won't come on sometimes, it could be due to over-heat, and a fan might help.
  3. k20a3 Valued Contributor ★ ★ ★ ☆ ☆

    Thanks jimjams, the compressor is fine and always comes on when needed. I wanted to know if the 6 times per hour was realistic or if I could push it harder?
  4. jimjams Club Member ★ ☆ ☆ ☆ ☆

    Right, I've been playing about with some numbers while Murray was being beaten by Djokovic

    The pressure of a gas = the density of the gas times the gas-constant of the gas times the absolute temperature of the gas

    P (in Pascal) = d (kg/m³) x R (J/kg.Kelvin) x T (Kelvin)

    R for air = 287 J/kg.Kelvin and T at room temperature = 293 Kelvin
    so R x T = ~84,00

    so P = d x 84,000

    the cut-out pressure = ~145 psi = 1,000,000 Pa
    the cut-in pressure = ~95 psi = 655,000 Pa

    d at 145 psi = 1,000,000 / 84,000 = 11.9 kg/m³
    d at 95 psi = 655,000 / 84,000 = 7.8 kg/m³

    volume of the air-tank = 200 litres = 0.2 m³

    mass of air at 145 psi = 11.9 x 0.2 = 2.38 kg
    mass of air at 95 psi = 7.8 x 0.2 = 1.56 kg

    so the difference between 95 psi and 145 psi of air in 200 litres = 0.82 kg of air

    Air at stp (standard temp & pressure) = 1.225 kg/m³
    So the difference at stp = 0.82/1.225 = 0.669 m³ = 669 litres

    i.e. it requires 669 litres of air at stp to be pumped into a 200 litre container at 95 psi, to raise the pressure to 145 psi

    The spec for the pump is 18 cfm (cubic feet per minute) which is 510 litres per minute

    So it should take about 80 seconds for the pump to raise the pressure from 95 psi to 145 psi, so if you are dropping the pressure back to 95 psi in under 80 seconds the pump won't keep up.

    The duty cycle depends on how fast your air-tool "drains" air out of the air-tank, I suspect that the "6 times per hour" (once every 600 seconds) that you were told is a nominal time using an impact gun or inflating a tyre or similar .... 6 times per hour would be a re-charge on usage of about 1 litre of air per second (expanded back into the atmosphere)

    Note that these are theoretical calculations, and could be some way out ...but it was more interesting than watching Tennis LOL
    k20a3 likes this.
  5. k20a3 Valued Contributor ★ ★ ★ ☆ ☆

    Wow not the answer I expected. But still a great explanation!

    So I timed it today and actually I was able to run the tools for about 2:30 mins. Longer than I thought.

    The pump has no problem keeping up with me, I suppose I just want make sure I don't over do it.
    Out of interest I tried just a home fan on it today and it cools down a lot quicker! I may put together a much more powerful one for those times when I need to keep it going.
    Many thanks for your equations :Smile:
  6. jimjams Club Member ★ ☆ ☆ ☆ ☆

    I'd be interested to see how long it takes to pump up the pressure from 95 psi to 145 psi.
    If I've interpreted "18 cfm" correctly, it should be about 80 seconds.

    But you're correct in using a fan to keep it cool, because it has a thermal overload protection, so it will cut-out if it gets too hot.
    k20a3 likes this.
  7. k20a3 Valued Contributor ★ ★ ★ ☆ ☆

    Well I went to screw fix and bought a big floor fan and mounted it onto the side of my compressor. If i am going to be using the compressor for quite a bit I put the fan on and leave it on. It cools down much faster between cycles which is just what I hoped for. I used some cardboard sheets temporarily to make a cowling to force the air over the cooling fins. Very affordable little solution.
    SpeedyGee and jimjams like this.