Hi friends, i have been working for 3 days to run my mini water pump with Arduino Uno + (5V DC Relay) + (6V DC pump).
1K resistor, BC547 transistor, 1N4007 diode. External power source is a basic 1.5V to 12V plug adaptor (I tried with 9V battery also).
First, i tried with 6V then 7.5V, 9V, 12V.
I feel the energy on the pump, tries to wheel but couldn't! What could be the reason?
[Solution]: You may need silicone oil for these pumps.
Thanks in advance.
Schematic?
Firstly have you tried the pump directly connected to the 6V power supply? Does it work then?
It claims to only need 30mA so the transistor should be able to switch it directly.
@dc42 I tried to follow this schematic Arduino Playground - HomePage.
Relay is working (clicking on-off by arduino).
@MarkT Now, i tried directly with the adaptor but the result is the same! It is trying to wheel but couldn't.
So is the motor or the adapter are broken? Measure the voltage when the motor is connected perhaps?
I tried to measure the adaptor, it says 18V mostly.. Sometimes it doubles the current level..I choose 1.5V and it says 4V for example.
It has still been so HOT although i unplugged it 10-15 min. ago. So, we can say that adaptor is broken 
I also measured my 9V rectangle battery and it says 8V.
Connected to the motor (that 6V pump) but the result is the same. Is it because too high to run it?
Sorry friends, i think my battery is also empty (but i don't know why multimeter says 8V).
A broken adaptor and emty battery, what a luck. And tomorrow is sunday.
Do you know any product to solve all this adaptor problem. Because i will have 4 pumps, should i use 4 different adaptors?
A product which can give 4-5 seperate 6 volts ?
Sorry, i am total newbie
Use one supply for 4 motors (4 X 0.03=120ma).
6 Volts rated at 500ma would work.
Maybe get a 6 V at 1 amp, for future enhancements.
Can you please explain a bit? (Or what should i learn to make this)
What is the supply? How can i set the Volt and the Amper?
This is a 5Volt 2 amp power supply.
This would be able to power your 4 motors with power to spare.
Of course your motor is 6 volts so it will be a bit slower with 5 volts.
You don't set the amps for a motor. You use the proper voltage that the motor is rated for, and knowing how much amperes the motor is rated to require maximum, you use a power supply capable of more current.
The motor will only draw as much current as it is designed for. Use a 6V 1A motor on a 6V power supply rated to put out a max of 10A, the motor still only draws 1A.
I deleted my message after seeing your message @polymorph 
Thank you.
I was asking that "may higher amperage damage the parts?"
Thank you all friends, really helped so much.
Oh, man, don't delete your messages. There is no shame in learning, and it puts other comments out of context.
BTW, I like that pump. I have an application requiring a lot of small peristaltic pumps, those would do nicely.
I found the best price on ebay for the pumps. I am usually getting my parts from aliexpress.com.
There is also solenoid type pumps which i don't exactly know what is the difference between peristaltic and solenoids. I will also buy one and test in the future
I have a pump like this, 5 Volts will not damage this pump.
Friends, how can we share "high ampers" in a circuit?
Is it like breadboard's power channel ? And all parts getting from there?
Friends, how can we share "high ampers" in a circuit?
Electronic components draw the current they do based on the resistance they have.
I want to share the news.
I found another 7.2V - 250A adaptor, and it was the same weak vibration without any spinning.
Then i opened the cover and remove the silicone tube. Without that tubing, It is working so fast!
I think the tube is so thick and don't let the motor work. Asked the seller but i don't think he will give me a solution.
Maybe i would try another silicon tubes. Bad luck.
A sort of lubricant for silicone would do the trick. Used the peristaltic pumps in my setup and had the same sort of problem. First disassembled the pump head and the tubing was jammed in between the rollers... When I fixed that the pump started to turn, but very slowly. Though the motor runs very fast when removed from the pump head... After injecting the pump head with a lubricant the motor ran at a nice speed 
See if that works...